2. BACKGROUND OF THE INVENTION Alzheimer's disease (AD) affects approximately 5- 15% of the population of the U.S. over age 65 (1.24 million).

This disease is frequently associated with individuals over the age of 60 and is the most frequent cause of institutionalization for long-term care. In 1983, more than $27 billion was spent in the U.S. in health care for Alzheimer's afflicted individuals.

Six basic areas of investigation have been defined by R.J. Wurtman, Scientific Amer., 62 (1985), as underlying most research on the causes of Alzheimer's disease. These areas include faulty genes, accumulations of amyloid protein, infectious agents, environmental toxins (e.g., aluminum and certain unusual amino acids), inadequate blood flow and energy metabolism, and lastly, cholinergic deficits.

A number of possible therapeutic interventions are currently under study. These include the use of nerve growth factors (NGF), muscarinic and nicotinic agonists, acetylcholinesterase (AChE) inhibitors, GABA-inverse agonists, NMDA modulators, and others. It is, however, unlikely that any single drug will restore cognition, especially in view of the involvement of a number of different neurotransmitter systems in memory processing, and the fact that dead neurons cannot be replaced.

While it is known that defects in neurotransmitter systems other than cholinergic system play a role in the

memory loss associated with AD, findings by K.L. Davis, presented at "New Strategies for the Treatment of Alzheimer's Disease," NIA Meeting (Jan. 8-10, 1990) indicated that administration of AChE inhibitors, such as physostigmine, result in modest cognitive improvement, and may prove useful for treating AD when administered in combination with other drugs such as clonidine, deprenyl or desipramine.

To the extent ACHE inhibitors can serve as useful adjuncts in the treatment of AD, two relatively new lycopodium alkaloids, (-)-huperzine A and B, isolated from Huperzia serrata (Thunb.) Trev., a Chinese folk medicine, appear superior to THA and physostigmine. U.S. Patent No.

5,177,082 to Yu et al.; J.S. Liu et al., Can. J. Chem., 64, 837 (1986); W.A. Ayer et al., ibid., 67, 1077 (1989), ibid., 67, 1538 (1989). The structure of (-)-huperzine A is depicted below: (-)-Huperzine A In studies performed in China, these compounds have been found to improve memory and learning in animals. X.C.

Tang et al., Acla Pharmacol. Sini, 7, 507 (1986).

Additionally, (-)-huperzine A has been studied by workers at Hoffman LaRoche in mice and squirrel monkeys, and the compound has been found to be an effective cognition enhancer. G.P. Vincent et al., Neurosci. Abst., 13, 884 (1987). The duration of action of a single dose (2 mg/kg i.m.) of (-)-huperzine A is over 6 hr, a remarkable result in relation to the AChE inhibitory action of physostigmine

(0.65 mg/kg i.m.), which has a maximal duration of action of 60 min and which causes considerable side effects. X.C. Tang et al., J. Neurosci. Res., 24, 276 (1989). (-)-Huperzine A has been further tested in 128 patients suffering from myasthenia gravis and found to control the clinical manifestations of the disease in 99% of these cases. Y.S.

Cheng, New Drugs and Clinical Remedies, 5, 197 (1986).

In addition, analogs of huperzine A have been reported. For example, A.P. Kozikowski et al. (U.S. Pat.

No. 4,929,731) disclose the analog of huperzine A, wherein the amino group has been replaced by -CH2NH2. A.P. Kozikowski (U.S. Pat. No. 5,104,880) discloses analogs of huperzine A wherein the C8-C15 double bond and the C15-methyl group are absent. A.P. Kozikowski et al. (U.S. Pat. No. 5,547,960) discloses C10-substituted analogs of huperzine A.

However, pharmacological agents that circulate systemically but that are targeted to brain tissue have enjoyed only limited success. For such pharmacological agents to enter brain tissue in therapeutically effective concentrations, the blood-brain barrier ("BBB") - a network of tightly joined endothelial cells of central nervous system capillaries - must first be penetrated. Because the membranes of the endothelial cells are phospholipoidal in nature, pharmacological agents that are lipophilic in nature are better able to diffuse through the BBB than those that are not (see Marcus E. Brewster et al., Chemical Approaches to Brain-Targeting of Biologically Active Compounds, in Drug Design for Neuroscience 435-67 (Alan P. Kozikowski ed., Raven Press, Ltd. 1993).

An approach taken to enhance the lipophilicity of pharmacological agents has been to convert the pharmacological agents into lipophilic "prodrugs." Such prodrugs, by virtue of their being more lipophilic than the particular pharmacological agents themselves, can more easily penetrate the BBB. Once within the brain parenchyma, the prodrugs are converted, generally enzymatically, back to the original pharmacological agent. To obtain lipophilic

prodrugs, pharmacological agents that bear hydroxyl, amino or carboxylic acid groups can be esterified or amidated with reactive species that contain hydrophobic moieties (Id. at 436). In addition, because in vivo conversion of a prodrug to its active pharmacological form generally occurs over a period of time, rather than instantaneously, the use of prodrugs offers the patient or subject the benefit of a sustained release of the pharmacological agent, generally resulting in a longer duration of action.

Unfortunately, indiscriminate selection of such reactive species can result in the formation of prodrugs having important limitations. First, prodrugs that contain certain easily cleavable groups are susceptible to hydrolysis during formulation and storage as well. On the other hand, prodrugs that were hydrophobically modified with groups that resist cleavage may be stable to intracellular esterases, precluding their conversion to therapeutically effective amounts of the active pharmacological agents.

Accordingly, there remains a need for pharmacologically active compounds that are targeted to and are capable of acting within brain tissue, that are sufficiently lipophilic to pass through the BBB in therapeutically effective concentrations, that are readily hydrolyzed to pharmacological agents in vivo and are stable to formulation and storage.

Citation or identification of any reference in Section 2 of this application shall not be construed as an admission that such reference is available as prior art to the present invention.

3. SUMMARY OF THE INVENTION The present invention provides huperzine A derivatives having the formula (I), methods for their synthesis, pharmaceutical compositions comprising the huperzine A derivatives, as well as methods for their use.

Particularly, the present invention provides huperzine A derivatives having the formula (I):

wherein X is selected from the group consisting of 0 and S; Y is selected from the group consisting of -O-, -S-, -CH2-, -CH(R)-, -C(R)(R)-, -CH=CH-, -C(R)=CH-, -CH=C(R)-, -C(R)=C(R)-, -NH- and -N(R)-; p is 0 or 1; and each R is independently selected from the group consisting of phenyl, C2-C24 alkyl, C2-Q4 alkenyl, C2-C24 alkynyl, C3-C24 cycloalkyl, C3-C24 cycloalkenyl, adamantyl, bicyclo(m.n.o.)alkyl and all positional isomers of furyl, thienyl, quinolyl, isoquinolyl, indolyl, naphthyl, anthracenyl, biphenylyl, tetrahydronaphthyl, indanyl, phenanthrenyl, pyrrolyl, imidazolyl, pyrazolyl, pyridyl, pyrazinyl, pyrimidinyl, pyridazinyl, isoxazolyl, isothiazolyl, imidazolidinyl, pyrazolidinyl, piperidinyl, piperazinyl and morpholinyl; m, n and o are independently an integer from 0 to 10, where 2 < m + n + o < 24; each of said R being unsubstituted or substituted with one or more halogen, CFl, phenyl, C-C8 alkyl, C2-C8 alkenyl, C2-C8 alkynyl, -OH, -OC-C8 alkyl, -OC2-C8 alkenyl, -OC2-C, alkynyl, -OC(O)C1-C8 alkyl, -OC(O)C2-C8 alkenyl, -OC(O)C2-C8 alkynyl, -SH, -SC-C8 alkyl, -SC2-Cg alkenyl, -SC2-C8 alkynyl, -SC(O)C-Cg alkyl, -SC(O)C2-C8 alkenyl, -SC(O)C2-C8 alkynyl, -CN, -NO2, -C(O)C1-C8 alkyl, -C(O)C2-C8 alkenyl, -C(O)C2-Cx alkynyl, -COH, -CO2C1-C8 alkyl, -CO2C2-C8 alkenyl,

-CO2C2-Cg alkynyl, -NH2, -NH(C,-Cx alkyl), -N(C-C8 alkyl)(C1-C8 alkyl), -NH3+, -N+(CI-C8 alkyl)(C-C8 alkyl)(C1-C8 alkyl), -C(O)NH2, -C(O)NH(C1-C8 alkyl) , -C(O)N(C1-C8 alkyl)(C-C8 alkyl) -S(O)CI-C8 alkyl, -S(O)C2-C8 alkenyl, -S(O)C2-CS alkynyl, -SO3H, -SO2C-Cx alkyl, -SO2C2-C8 alkenyl and -SO2C2-C8 alkynyl groups; and when p = 0 and X = O, -C(=X)-R can additionally be the C-terminus of an amino acid or peptide; and pharmaceutically acceptable salts thereof.

The compounds of formula (I) are capable of inhibiting AChE and treating Alzheimer's dementia, myasthenia gravis, an age-related memory impairment, Down's syndrome and glaucoma.

Preferably, the compound of formula (I) is selected from the group consisting of: O-pivaloylhuperzine A; O-(1-adamantoyl)huperzine A; O-(n-Caproyl)huperzine A; O-(n-Capryloyl)huperzine A; O-(n-Capryl)huperzine A; O-(n-Lauryl)huperzine A; O-(n-Myristyl)huperzine A; O-(n-Palmityl)huperzine A; O-(n-Stearyl)huperzine A; O-(Linoleyl)huperzine A; O-(Linolenyl)huperzine A; O-(Acetylsalicylyl)huperzine A; O-(o-toluoyl)huperzine A; 0-(2,4,6-trimethoxybenzoyl)huperzine A; 0-(nicotinoyl) huperzine A; O-(O-acetylmandelyl)huperzine A; 0-(2,2-dimethyl-3-phenylpropionyl)huperzine A; O-(l-methyl-1-cyclohexanecarbonyl)huperzine A; O-(isobutyryl)huperzine A; O-(endo-norbornane-2-carbonyl)huperzine A; O-(tert-butoxycarbonyljhuperzine A; and O-(cholinecarbonyl)huperzine A.

The invention further provides pharmaceutical compositions comprising a compound of formula (I) and a pharmaceutically acceptable carrier or vehicle. Such compositions are useful for inhibiting AChE, and treating Alzheimer's dementia, myasthenia gravis, an age-related memory impairment, Down's syndrome and glaucoma.

The invention still further provides a method for inhibiting AChE in a mammal comprising administering to the mammal in need of said AChE inhibition, a therapeutically effective amount of a composition comprising a compound of formula (I).

The invention still further provides a method for treating a disorder in a mammal, the disorder selected from the group consisting of Alzheimer's dementia, myasthenia gravis, an age-related memory impairment, Down's syndrome and glaucoma, comprising administering to the mammal in need of such treatment, a therapeutically effective amount of the composition comprising a therapeutically effective amount of a compound of the formula (I).

The invention still further provides a method for the synthesis of a compound of formula (I) comprising the step of contacting huperzine A with a compound selected from the group consisting of formula (IIa) and formula (IIb): R-N=C=O (IIb), wherein Z is -OH or a leaving group.

The present invention can be understood more fully by reference to the following detailed description and illustrative examples that are intended to exemplify non- limiting embodiments of the invention.

4. DETAILED DESCRIPTION OF THE INVENTION 4.1 HUPERZINE A DERIVATIVES OF FORMULA (I) In accordance with the present invention, the huperzine A derivatives (the "compounds of formula (I)") useful for inhibiting AChE and treating Alzheimer's dementia, myasthenia gravis, an age-related memory impairment, Down's syndrome and glaucoma are represented by formula (I): wherein X is selected from the group consisting of 0 and S; Y is selected from the group consisting of -O-, -S-, -CH2-, -CH(R)-, -C(R)(R)-, -CH=CH-, -C(R)=CH-, -CH=C(R)-, -C(R)=C(R)-, -NH- and -N(R)-; p is 0 or 1; and each R is independently selected from the group consisting of phenyl, C2-C4 alkyl, C2-C24 alkenyl, C2-C24 alkynyl, C3-C24 cycloalkyl, C-C24 cycloalkenyl, adamantyl, bicyclo(m.n.o.)alkyl and all positional isomers of furyl, thienyl, quinolyl, isoquinolyl, indolyl, naphthyl, anthracenyl, biphenylyl, tetrahydronaphthyl, indanyl, phenanthrenyl, pyrrolyl, imidazolyl, pyrazolyl, pyridyl, pyrazinyl, pyrimidinyl, pyridazinyl, isoxazolyl, isothiazolyl, imidazolidinyl, pyrazolidinyl, piperidinyl, piperazinyl and morpholinyl; m, n and o are independently an integer from 0 to 10, where 2 < m + n + o < 24;

each of said R being unsubstituted or substituted with one or more halogen, CF3, phenyl, C1-C8 alkyl, C2-C8 alkenyl, C2-C8 alkynyl, -OH, -OC-Cx alkyl, -OC2-C8 alkenyl, -oC2-C8 alkynyl, -OC(O)C1-C8 alkyl, -OC(O)C2-C8 alkenyl, -OC(O)C2-C8 alkynyl, -SH, -SC-C8 alkyl, -SC2-C8 alkenyl, -SC2-C8 alkynyl, -SC(O)C-Cg alkyl, -SC(O)C2-C8 alkenyl, -SC(O)C2-C8 alkynyl, -CN, -NO2, -C(O)C-Cx alkyl, -C(O)C2-Cg alkenyl, -C(O)C2-Cx alkynyl, -CO2H, -CO2C1-C8 alkyl, -CO2C2-C8 alkenyl, -CO2C2-Cx alkynyl, -NH2, -NH(C,-Cx alkyl), -N(C-Cx alkyl)(C-C8 alkyl), -NH3+, -N+(C-CX alkyl)(C-Cx alkyl)(C-Cx alkyl), -C(O)NH2, -C(O)NH(C-Cx alkyl) , -C(O)N(C-Cx alkyl) (C1-C, alkyl) -S(O)C-C alkyl, -S(O)C2-Cx alkenyl, -S(O)C2-Cx alkynyl, -SO3H, -SO2C1-C8 alkyl, -SO2C2-Cx alkenyl and -SO2C2-Cx alkynyl groups; and when p = 0 and X = O, -C(=X)-R can additionally be the C-terminus of an amino acid or peptide; and pharmaceutically acceptable salts thereof.

Any pharmaceutically acceptable salt known, or to be developed, can be utilized and include, but are not limited to, those derived from inorganic acids such as hydrochloric, hydrobromic, sulfuric, sulfamic, phosphoric, carbonic, nitric and the like; and those prepared from organic acids such as acetic, propionic, succinic, glycolic, stearic, lactic, malic, tartaric, citric, ascorbic, pamoic, maleic, hydroxymaleic, phenylacetic, glutamic, benzoic, salicylic, sulfanilic, 2-acetoxybenzoic, fumaric, toluenesulfonic, methanesulfonic, ethanedisulfonic, oxalic, isethionic, trifluoroacetic, gluconic and the like. Such salts can be prepared, for example, according to Examples 7 and 8 of U.S. Patent No. 4,383,114 to Vince, or by other methods commonly known to those skilled in the art.

It is to be pointed out that when such acid salts are employed, the salts may be prone to accelerated decomposition and accordingly, prolonged storage thereof should be avoided.

When R is substituted with one or more -NH3+ or

-N+(C1-C, alkyl)(C-Cg alkyl)(CI-Cg alkyl), the counter ion associated with the -NH+ or -N+(C-C alkyl)(C-Cg alkyl)(C-C8 alkyl) group is a conjugate base of an acid described above.

"C2-C24 alkyl" is meant to include straight- and branched-chain saturated aliphatic hydrocarbon groups having 2-24 carbon atoms including, but not limited to, ethyl, n- propyl, isopropyl, n-butyl, isobutyl, sec-butyl, t-butyl, n- pentyl, neopentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, octadecyl, nonadecyl, eicosyl, heneicosyl, docosyl, tricosyl, tetracosyl and the like.

"C2-C24 alkenyl" is meant to include straight- and branch chain hydrocarbon groups having at least one double bond and including, but not limited to, vinyl, allyl, isoprenyl, 1-propenyl, 2-butenyl, 2-methyl-2-butenyl, pentenyl, hexenyl, heptenyl, farnesyl, geranyl, geranylgeranyl and the like.

"C2-C24 alkynyl" is meant to include straight- and branch chain hydrocarbon groups having at least one triple bond and including, but not limited to, propargyl.

"C3-C24 cycloalkyl" is meant to include non-aromatic, cyclic hydrocarbon groups including, but not limited to, cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cyclooctyl, cyclodecyl, cyclododecyl and the like.

"C3-C24 cycloalkenyl" is meant to include non- aromatic, cyclic hydrocarbon groups having at least one double bond and including, but not limited to, cyclopropenyl, cyclobutenyl, cyclopentenyl, cyclopentadienyl, cyclohexenyl, cyclohexadienyl, cycloheptenyl, cycloheptadienyl, cycloheptatrienyl and the like.

By "amino acid" is meant the L-, D- or racemic form of an a- or amino acid. Amino acids useful in this regard include, but are not limited to glycine, alanine, valine, leucine, isoleucine, proline, serine, threonine, phenylalanine, tyrosine, tryptophan, lysine, arginine,

histidine, aspartic acid, glutamic acid, asparagine, glutamine, cysteine, methionine and -alanine.

By "peptide" is meant a linear sequence of 2 or more amino acids joined via a peptide bond. Preferably, the number of amino acids in such a peptide ranges from 2 to about 20.

In addition to all of the possible combinations of C, X and R that are encompassed by the compounds of formula (I) when p = 0 or 1, it is to be pointed out that when p = 0 and X = O, -C(=X)-R can additionally be the C-terminus of an amino acid or peptide.

Preferably, -C(=X)-(Y),-R taken together form a radical selected from the group consisting of pivaloyl, 1- adamantoyl, n-caproyl, n-capryloyl, n-capryl, n-Lauryl, n- myristyl, n-palmityl, n-stearyl, linoleyl, linolenyl, acetylsalicylyl, o-toluoyl, 2,4,6-trimethoxybenzoyl, nicotinoyl, O-acetylmandelyl, 2,2-dimethyl-3-phenylpropionyl, l-methyl-l-cyclohexanecarbonyl, isobutyryl, endo-norbornane- 2-carbonyl, -C(O)OC(CH)3 and -C(O)OCH2CH2N(CH3)3+, such that the compound of formula (I) is preferably selected from the group consisting of O-pivaloylhuperzine A, 0-(1- adamantoyl)huperzine A, O-(n-caproyl)huperzine A, O-(n- capryloyl)huperzine A, O-(n-capryl)huperzine A, O-(n- lauryl)huperzine A, O-(n-myristyl)huperzine A, O-(n- palmityl)huperzine A, O-(n-stearyl)huperzine A, O- (linoleyl)huperzine A, O-(linolenyl)huperzine A, O- (acetylsalicylyl)huperzine A, O-(o-toluoyl)huperzine A, O- (2,4,6-trimethoxybenzoyl)huperzine A, O-(nicotinoyl)huperzine A, O-(O-acetylmandelyl)huperzine A, 0-(2,2-dimethyl-3- phenylpropionyl)huperzine A, O-(l-methyl-l- cyclohexanecarbonyl)huperzine A, O-(isobutyryl)huperzine A, O-(endo-norbornane-2-carbonyl)huperzine A, O- (tert- butoxycarbonyl)huperzine A and O-(cholinecarbonyl)huperzine A, respectively.

It is to be understood that the compounds of formula (I) can exist in either racemic, i.e., (+)form, or

in the form of optical isomers, i.e., in the (+)- or (-)- form.

Without being bound by any particular theory, it is believed that the compounds of formula (I), by virtue of the fact that they comprise groups defined by "R," above, are better able than huperzine A to transverse the BBB. Once in the brain parenchyma, it is believed that the compounds of formula (I) accumulate within "depots," i.e., fatty domains of the brain, in particular within cell membranes. In such depots, the compounds of formula (I) act to inhibit AChE, and treat Alzheimer's dementia, myasthenia gravis, an age-related memory impairment, Down's syndrome and glaucoma.

In addition, it is believed that within the depots, the compounds of formula (I) slowly hydrolyze in the presence of brain esterases or other enzymes to provide huperzine A, which is capable of inhibiting AChE and treating Alzheimer's dementia, myasthenia gravis, an age-related memory impairment, Down's syndrome and glaucoma. Thus, it is believed that the compounds of formula (I) behave as prodrugs of huperzine A. As used herein, by "prodrug" is meant a derivative of huperzine A which, when administered to a mammal, especially a human, is hydrolyzed by esterases or other hydrolytic enzymes endemic to brain or other tissue, so as to make huperzine A available at its target site(s). The slow hydrolysis of the compounds of formula (I) is believed to offer a desirable "slow release" of huperzine A from the compounds of formula (I).

Furthermore, unlike huperzine A, which is not metabolized by mammals, but rather is excreted without production of active metabolites, the compounds of formula (I) are believed to remain in circulation in the body and reside in brain depots for relatively longer periods of time, until they are hydrolyzed by the enzymes described above, releasing huperzine A. It is believed that the combination of enhanced BBB transversal and brain residence properties leads to longer duration of action of huperzine A, relative to huperzine A that is administered in its non-derivative

form, which lessens the number of daily doses of huperzine A a patient or subject would otherwise require for the treatment of Alzheimer's dementia, myasthenia gravis, an age- related memory impairment, Down's syndrome and glaucoma.

Still further, it is believed that the improved delivery of the compounds of formula (I) to the brain, relative to huperzine A, lessens the incidence and severity of undesirable side effects of huperzine A administration, such as dizziness and nausea.

4.2 SYNTHESIS OF THE HUPERZINE A DERIVATIVES OF FORMULA (I) The compounds of formula (I) can be obtained by contacting huperzine A, either in the form of its racemate, (+)-enantiomer or (-)-enantiomer, with an acylating agent selected from the group consisting of formula (IIa) and formula (IIb): R-N=C=O (IIb), wherein Z is -OH or a leaving group; and R, Y, p, and X are defined as above in formula (I).

Accordingly, the compounds of formula (IIa) and formula (IIb), are useful as intermediates for obtaining the compounds of formula (I) which are capable of inhibiting AChE, and treating Alzheimer's dementia, myasthenia gravis, an age-related memory impairment, Down's syndrome and glaucoma.

General examples of compounds of formula (IIa) can be found, for example, in J. Mulzer, Synthesis of Esters, Activated Esters and Lactones, in 6 Comprehensive Organic

Synthesis 323-80 (B.M. Trost et al. eds., 1991); and R.C.

Parish et al., J. Org. Chem. 30:927 (1965).

In the reaction of huperzine A with a compound of formula (IIa) wherein X = O, p = 1 and Y = -C(R)(R)-, -CH=CH-, -C(R)=CH-, -CH=C(R)- or -C(R)=C(R)-, preferable leaving groups are -OC6Fs (L. Kisfaludy et al., J.

Org. Chem. 44:654 (1979)), -OCF(CF3)2 (N. Ishikawa et al., Chem. Lett. 673 (1976)), benzotriazol-l-yloxy (S. Kim et al., J. Org. Chem. 50:1751 (1985)), N-methylpyridinio-2-oxy (T.

Mukaiyama, Angew. Chem., Int. Ed. Engl. 18:707-21 (1979) and K.C. Nicolaou, Chem. Eur. J. 1:454 (1995)), 2,4,6- trinitrophenoxy (S. Kim et al., Syn. Commun. 11:121 (1981)), 3,5-dinitro-2-pyridyloxy (S. Takimoto et al., Bull. Chem.

Soc. Jpn. 56:639 (1983)), 2-thioxothiazolidin-3-yl (S.

Yamada, J. Org. Chem. 57:1591 (1992)), cyanide (A. Holy et al., Tetrahedron Lett. 185 (1971) and M. Havel et al., Coll.

Czech. Chem. Commun. 44:2443 (1979)), 2-pyridylthio (E.J.

Corey et al., J. Am. Chem. Soc. 96:5614 (1974); E.J. Corey et al., J. Am. Chem. Soc. 97:653, 654 (1975); E.J. Corey et al., J. Am. Chem. Soc. 97:2287 (1975) and H. Gerlach et al., Helv.

Chim. Acta 57:2661 (1974) (in the presence of Ag+)), 1- alkylpyridinio-2-thio (T. Sakakibara et al., Bull. Chem. Soc.

Jpn. 61:247 (1988)) and C1-C4 alkoxy (J. Otera, Chem. Rev.

93:1449-70 (1993)).

In the reaction of huperzine A with a compound of formula (IIa) wherein X = O, p = 1 and Y = 0, preferable leaving groups are -Cl (such compounds are alkyl chloroformates, obtained by reaction between an alcohol and phosgene employing conditions known to those of ordinary skill in the art), -F (V.A. Dang et al., J. Org. Chem.

55:1847 (1990) and V.A. Dang et al., J. Org. Chem. 55:1851 (1990)) and -OC(O)OR, where R is defined above (E.M. Carreira et al., J. Am. Chem. Soc. 117:8106 (1995) and F. Houlihan et al., Can. J. Chem. 63:153 (1985)), where R is defined above.

In the reaction of huperzine A with a compound of formula (IIa) wherein X = O, p = 1 and Y = -N(R)-, a preferable leaving group is -Cl (L.C. Raiford et al., J. Org.

Chem. 5:300 (1940); J. Herzog, Ber. Dtsch. Chem. Ges. 40:1831 (1907) and F. Lustig et al. J. Org. Chem. 32:851 (1967)).

Alternatively, such compounds, known as N,N-dialkylcarbamoyl chlorides, can be obtained from the reaction of secondary amines with phosgene, employing reaction conditions known to those of ordinary skill in the art.

In the reaction of huperzine A with a compound of formula (IIa) wherein X = S, p = 1 and Y = -N(R)-, a preferable leaving group is -Cl (M.S. Newman et al. J. Org.

Chem. 31:3980 (1966); H.J. Kurth, Chem. Ber. 106:2419 (1973); B. Blank et al., J. Med. Chem. 17:1065 (1974); A. Kaji et al., Bull. Chem. Soc. Jpn. 44:1393 (1971); C.F. Reinecke et al., J. Org. Chem. 42:1139 (1977); M.S. Newman et al., Org.

Syn. 51:139 (1971); U. Kraatz et al., Chem. Ber. 110:1776 (1977); H-J. Kurth et al., Liebigs Ann. Chem. 1313 (1976); A.

Wagenaar et al., Recl.: J. R. Neth. Chem. Soc. 101:91 (1982) and H. Wolfers et al., Synthesis 43 (1975)). Alternatively, such compounds, known as N,N-dialkylthiocarbamoyl chlorides, can be obtained from the reaction of secondary amines with thiophosgene, employing reaction conditions known to those of ordinary skill in the art.

In the reaction of huperzine A with a compound of formula (IIa) wherein X = S, p = 1 and Y = -O-, a preferable leaving group is -Cl (D.L. Garmaise et al., J. Org. Chem.

27:4509 (1962) and S. Wakamori et al., Agric. Biol. Chem.

(Tokyo) 33:1700 (1969)).

In general, compounds of formula (IIa) where p = 0, X = 0 and Z = -OH, i.e., carboxylic acids, can be obtained according to methods disclosed in R.B. Wagner et al., Synthetic Organic Chemistry 411-78 (1953), as well as from hydrolysis of the corresponding esters (Id. at 479-532), amides (Id. at 565-589) and nitriles (Id. at 590-633).

In addition, such carboxylic acids can be obtained from oxidation of corresponding alcohols and aldehydes (Carruthers, Some Modern Methods of Organic Synthesis 338-55 (1978); and Chinn, Selection of Oxidants in Synthesis 63-70 (2d ed. 1971)); oxidation of aromatic and heteroaromatic

alkyl groups (Lee, The Oxidation of Organic Compounds by Permanganate Ion and Hexavalent Chromium 43-64 (1980)); carboxylation of Grignard and organolithium reagents (H.W.

Gschwend et al., Chem. Rev. 26:1-360 (1979); R.D. Clark et al., Chem. Rev. 47:1-314 (1995) and Volpin et al., Organomet.

React. 5:313-86 (1975)); malonic ester synthesis (Jerry March, Advanced Organic Chemistry: Reactions, Mechanisms, and Structure 412 (3d ed. 1985)); cyanoacetic ester synthesis (Id. at 413); acetoacetic ester synthesis (Id.), a-alkylation of esters, N-N-disubstituted amides and nitriles in the presence of strong bases such as sodium amide or lithium diisopropyl amide followed by hydrolysis (for nitriles: S.

Arseniyadis et al., Org. React. 31:1-364 (1984) and A.C. Cope et al., Org. React. 9:107-331 (1957); for esters: A.C. Cope et al., Org. React. 9:107-331 (1957); and for amides: P.C.

Kuzma et al., J. Org. Chem. 49:2015 (1984)); reaction of alkylhalides or alkylsulfonates with cyanide, followed by hydrolysis of the resulting nitrile (Friedrich et al., in The Chemistry of the Cyano Group 77-86 (1970) and Compagnon et al., Ann. Chim. (Paris) (14):11-22 and 23-37 (1970)); Sandmeyer reaction between arenediazonium salts and CuCN (March, supra, at 648); a, -unsaturated acids, esters and nitriles by Knoevenagel condensation (Id. at 835); a, - unsaturated esters by the Reformatsky reaction (Rathke, Org.

React. 22:423-60 (1975) and Gaudemar, Organomet. Chem. Rev.

Sect. A 8:183-233 (1972)); a, -unsaturated esters by the Wittig reaction (A. Maercker, Chem. Rev. 14:270-490 (1965)); a-hydroxyacids from hydrolysis of cyanohydrins obtained from aldehydes and cyanide (Friedrich in The Chemistry of Functional Groups, Supplement C 1345-90 (1983)); substituted cyclohexene- and cyclohexanecarboxylic acids from Diels-Alder reaction (March, supra, at 745); addition of cuprates to a,P- unsaturated esters and other similar species (G.H. Posner, Chem. Rev. 19:1-113 (1972)) and reaction of aryl, heteroaryl and vinyl halides with a, -unsaturated acids, esters and nitriles to form cinnamic acid derivatives and a, ;

diunsaturated acid derivatives (R.F. Heck, Chem. Rev. 27:345- 90 (1982)).

In the reaction of huperzine A with a compound of formula (IIa) wherein X = O, p = 1, Y = -CH(R)-, -C(R)(R)-, -CH=CH-, -C(R)=CH-, -CH=C(R)- or -C(R)=C(R)-, and Z = -OH, it is preferable that the reaction take place in the presence of an "activating agent" which is believed to react with the compounds of formula (IIa) to form an activated intermediate which reacts with huperzine A to form the corresponding compounds of formula (I).

Activating agents useful in this regard include methanesulfonyl chloride (S. Chandrasekaran et al., Syn.

Commun. 12:727 (1982)), trifluoromethanesulfonic anhydride (L. Brown et al., J. Org. Chem. 49:3875 (1984)), a carbodiimide such as dicyclohexylcarbodiimide, preferably in the presence of 4-dimethylaminopyridine (B. Neises et al., Angew. Chem., Int. Ed. Engl. 17:522 (1978); A. Hassner et al., Tetrahedron Lett. 4475 (1978); E.P. Boden et al., J.

Org. Chem. 50:2394 (1986) and L.J. Mathias, Synthesis 561 (1979)), 2,4,6-trifluorobenzoyl chloride (J. Inanaga et al., Bull. Chem. Soc. Jpn. 52:1989 (1979)), bis(2-oxo-3- oxazolidinyl)phosphinic chloride (J. Diago-Meseguer et al., Synthesis 547 (1980) and M. Ballester-Rodes et al., Syn.

Commun. 14:515 (1984)), diethylcyanophosphate (T. Shioiri et al., Tetrahedron 32:2211, 2854 (1976)), a dialkyl or diaryl chlorophosphate (T. Garcia et al., Syn. Commun. 12:681 (1982) and J.D. White et al., J. Org. Chem. 57:2270 (1992)), isopropenyl chloroformate (C. Zeggaf et al., Tetrahedron 45:5039 (1989)), trifluoroacetic anhydride (R.C. Parish et al. J. Org. Chem. 30:927 (1965) and T. Hattori et al.

Synthesis 41 (1995)), bromotripyrrolidinophosphonium hexafluorophosphate (J.L. Wood et al., J. Am. Chem. Soc.

114:5898 (1992)), carbonyldiimidazole (C.L. Brewer et al., Carbohydr. Res. 36:188 (1974)); S. Ohta et al., Synthesis 833 (1982); W.R. Roush et al., J. Org. Chem. 50:3224 (1985)), azole derivatives such as oxalyldiimidazole, oxalylditriazole and oxalylditetrazole (S. Murata, Bull. Chem. Soc. Jpn.

57:3597 (1984)) and carbonylditetrazole (J. Strawinsky et al., J. Chem. Soc., Chem. Commun. 243 (1976)).

When p = 0, X = 0 and Z = -OH, the compound of formula (IIa) can additionally be an amino acid or a peptide, such that -C(=X)-R is the C-terminus of the amino acid or peptide. In this case, the reaction of the amino acid or peptide with huperzine A will take place in the presence of an activating agent described above. Preferably, the amino acid or peptide will have a protecting group at its N- terminus and at other nucleophilic sites if present, which are optionally removed subsequent to the reaction of the amino acid or peptide with huperzine A. Examples of useful protecting groups are found in Theodora W. Greene, Protective Groups in Organic Synthesis 218-87 (1981). Useful peptides can be obtained according to the methods of Gross et al., 1-3 The Peptides (1979-81); Klausner et al., Synthesis 453-63 (1972); and Albertson, Org. React. 12:205-18 (1962).

Advantageously, the reaction of the compounds of formula (IIa) with huperzine A can take place in the presence of an acylation catalyst such as 4-dimethylaminopyridine, tributylphosphine (E. Vedejs et al., J. Am. Chem. Soc.

115:3358 (1993) and E. Vedejs et al., J. Org. Chem. 58:7268 (1993)), scandium trifluoromethanesulfonate (K. Ishihara et al., J. Am. Chem. Soc. 117:4413 (1995)) and P(NMeCH2CH2)3N (B.A. d'Sa et al., J. Org. Chem. 61:2963 (1996).

Compounds of formula (IIb) can be prepared according to the methods of Richter et al., in 2 The Chemistry of Cyanates and Their Thio Derivatives 619-818 (1977). The reaction between huperzine A and R-N=C=O preferably occurs in the presence of a reaction catalyst such as CuCl (M.E. Duggan et al., Synthesis 131 (1989)), BF3- etherate (H. Irie et al., J. Chem. Soc., Perkin Trans. 1 1209 (1989)) or n-butyllithium (A. Nikiforov et al., Liebigs Ann.

Chem. 489 (1989)).

It will be understood that the compounds of formula (I) that are obtained by acylating (+)-huperzine A will be racemic, and the compounds of formula (I) that are obtained

by acylating (+)-huperzine A or (-)-huperzine A will have the same degree of optical purity as either the (+)-huperzine A or (-)-huperzine A starting material. Mixtures of (+)- and (-)-huperzine having an enantiomeric excess of either the (+)- or (-)-enantiomer can also be used in this regard.

Accordingly, the reaction of (+)-huperzine A with the compounds of formula (IIa) or formula (IIb) will result in compounds of formula (I) that are racemic. In addition, the reaction of (+)-huperzine A with the compounds of formula (IIa) or formula (IIb) will result in compounds of formula (I) that possess the same absolute configuration as (+)- huperzine A, and the reaction of (-)-huperzine A with the compounds of formula (IIa) or formula (IIb) will result in compounds of formula (I) that possess the same absolute configuration as (-)-huperzine A. Furthermore, the reaction of a mixture of (+)- and (-)-huperzine having an enantiomeric excess of the (+)-enantiomer with the compounds of formula (IIa) or formula (IIb) will result in compounds of formula (I) that have an enantiomeric excess of the compound of formula (I) that is derived from the (+)-enantiomer. Still further, the reaction of a mixture of (+)- and (-)-huperzine having an enantiomeric excess of the (-)-enantiomer with the compounds of formula (IIa) or formula (IIb) will result in compounds of formula (I) that have an enantiomeric excess of the compound of formula (I) that is derived from the (-)- enantiomer.

(+)-Huperzine A can be obtained according to the procedures described in A.P. Kozikowski et al., J. Am. Chem.

Soc. 111:4116 (1989); A.P. Kozikowski et al., J. Chem. Soc., Perkin Trans. I 195 (1990); A.P. Kozikowski et al., J. Chem.

Soc., Chem. Commun. 860 (1993); G. Campiani et al., J. Org.

Chem. 58:7660 (1993); U.S. Patent No. 4,929,731 to Kozikowski et al.; and U.S. Patent No. 5,106,979 to Kozikowski et al.

(-)-Huperzine A can be isolated from Huperzia serrata (U.S. Patent No. 5,177,082 to Yu et al.; and J-S. Liu et al., Can. J. Chem. 64:837-39 (1986)); or synthesized according to the procedures described in F. Yamada et al., J.

Am. Chem. Soc. 113:4695-96 (1991); and S. Kaneko et al., Tetrahedron: Asymmetry 8(6) :829-32 (1997)).

(+)-Huperzine A can be synthesized according to methods disclosed in F. Yamada et al., J. Am. Chem. Soc.

113:4695-96 (1991), or obtained via an enantiomeric resolution using chiral high-performance liquid chromatography according to the method of McKinney et al., Eur. J. Pharwacol. 203:303 (1991).

As used herein, the term "huperzine A," when not preceded by "(+)-," "(+)-" or "(-)-," encompasses (+)-, (+)- and (-)-huperzine A.

The compounds of formula (I) can be obtained by reacting from about 1 to about 2 equivalents, preferably from about 1 to about 1.5 equivalents and more preferably from about 1 to about 1.2 equivalents of a compound of formula (IIa) or formula (IIb) with about 1 equivalent of huperzine A, preferably in the presence of about 1 to about 10 equivalents of an organic base such as pyridine, 4- (dimethylamino)pyridine, DBU, triethylamine, imidazole, lutidine, collidine, methylamine, diisopropylethylamine, di- tert-butylamine and the like, and mixtures thereof; or an inorganic base such as an alkali metal alkoxide, an alkyllithium reagent, lithium diisopropylamide, an alkali metal hexamethyldisilazide, an alkali metal hydride and the like. Preferably, from about 0.01 equivalents to about 0.2 equivalents of 4-(dimethylamino)pyridine are used in conjunction with the amine base described above. Without being bound to any particular theory, the organic base scavenges acids liberated in the reaction between the compound of formula (IIa) or formula (IIb) and huperzine A, and the inorganic base deprotonates the amide nitrogen atom of huperzine A, converting its C-I carbonyl group to an enolate and a relatively stronger nucleophile.

Advantageously, the reaction between huperzine A and the compound of formula (IIa) or formula (IIb), preferably in the presence of the organic base, takes place in the presence of an organic solvent. Such organic solvents

useful in this regard include, but are not limited to, dichloromethane, chloroform, diethyl ether, tetrahydrofuran, dimethylformamide, benzene, toluene and the like.

Preferably, the organic solvent is dichloromethane or, if an alkali metal base is used, tetrahydrofuran. Generally, when organic solvent is used, the mixture of huperzine A, compound of formula (IIa) or formula (IIb), and optionally organic base, form a mixture that is about 10 to about 70 weight percent, relative to the organic solvent.

As used herein, "reagent" is meant to encompass huperzine A, a compound of formula (IIa), a compound of formula (IIb), organic base and organic solvent. While the particular sequence of reagent addition is not critical to the synthesis of the compounds of formula (I), preferably, the compound of formula (IIa) or formula (IIb) is added to a huperzine A which is optionally in the presence of organic base and organic solvent. Reagent addition can occur at a temperature from about -780C to about 500C, preferably from about -250C to about room temperature, and most preferably at about room temperature.

Following the addition of the reagents, the reaction mixture is allowed to stir at the temperature of reagent addition or preferably, at a higher temperature, until the formation of a compound of formula (I) is complete.

Preferably, the addition of reagents takes place at about 0°C, and the reaction mixture is allowed to stir at about room temperature. The progress of the reaction between huperzine A and the compound of formula (IIa) or formula (IIb) can be monitored using thin layer chromatography, high performance liquid chromatography, or other means known to those skilled in the art.

When the formation of a compound of formula (I) appears to be complete, the reaction mixture which contains the compound of formula (I) can be purified via recrystallization, silica gel chromatography, high performance liquid chromatography, or other means known to those skilled in the art. Preferably, the reaction mixture

is concentrated, i.e., volatiles such as organic solvent and organic base are removed therefrom, prior to purification.

Optionally, and adsorbent such as ELITES (silicon dioxide) or silica gel can be added to the reaction mixture just prior to concentration, and the resulting mixture concentrated such that the compound of formula (I) is adsorbed onto the surface of the adsorbent. The adsorbent which contains the compound of formula (I) can then be added directly to a silica gel- filled column for purification.

It must be pointed out that huperzine A contains three nucleophilic groups, namely a primary amino group at C- 13, a pyridone nitrogen atom and a pyridone carbonyl oxygen atom at C-l. Prior to the present invention, it would have been predicted by one of skill in the art that the three nucleophilic groups of huperzine A would compete with one another for reaction with the compounds of formula (IIa) and formula (IIb). Surprisingly and unexpectedly, using the reaction conditions disclosed herein, the compounds of formula (IIa) and formula (IIb) react predominantly with the C-l pyridone carbonyl oxygen atom of huperzine A, with little competition from side reactions, and with only minor reaction with either the C-13 amino group or the pyridone nitrogen atom. Accordingly, the compounds of formula (I) can be obtained directly from huperzine A and compounds of formula (IIa) or formula (IIb) without the need for using protecting groups for the C-13 amino group and the pyridone nitrogen atom, providing highly desirable time- and cost-saving benefits, as well as increased yield of product as a result of requiring fewer synthetic steps.

It is to be pointed that any C-13 or pyridone N- acylated side reaction product formed from the reaction between huperzine A and the compound of formula (IIa) or formula (IIb) and can be purified from the desired compounds of formula (I) using chromatography, including silica gel and high-performance liquid chromatography, or crystallization.

4.3 METHODS FOR USE OF THE COMPOUNDS OF FORMULA (I) The compounds of formula (I) are useful for inhibiting AChE. Compounds that inhibit AChE are useful as pharmaceutical agents for treating mammals, especially humans, for the treatment of disorders wherein AChE is involved, e.g., in clinical settings, for the treatment of memory and learning disorders. Such conditions include Alzheimer's dementia (AD), myasthenia gravis, and other age- related memory impairments. In addition, the compounds of formula (I) can be used to treat Down's syndrome and glaucoma.

Accordingly, the compounds of formula (I) are useful for the treatment of any disorder known or to be discovered wherein inhibition of AChE results in treatment of the disorder. Such disorders include memory and learning disorders, including AD, myasthenia gravis, and other age- related memory impairments. In addition, the compounds of formula (I) are believed to offer the added advantage of being more readily capable of traversing the BBB, and being capable of residing in brain depots for longer periods of time, relative to huperzine A. It is believed that these advantages lead to a longer duration of action, relative to huperzine A, which lessens the number of daily doses of huperzine A a patient or subject would otherwise require for the treatment of Alzheimer's dementia, myasthenia gravis, an age-related memory impairment, Down's syndrome and glaucoma.

When administered to a mammal for veterinary use or to a human for clinical use, the compounds of formula (I), or mixtures thereof, can be used alone, or in combination with any physiologically acceptable carrier or excipient suitable for enteral or parenteral administration. Suitable mammals include, for example, dogs, particularly those used as guides for the sight-impaired, and humans. Where used for parenteral administration, the physiologically acceptable carrier must be sterile and suitable for in vivo use in a human, or for use in a veterinary clinical situation.

The compounds of formula (I) can be used in the form of a pharmaceutical preparation, for example, in solid, semisolid or liquid form, which contains at least one of the compounds of formula (I), including their therapeutically active salts, as a bioactive component, alone or in combination with another AChE inhibiting compound such as physostigmine, clonidine, deprenyl or desipramine, in admixture with a carrier or an excipient suitable for enteral or parental administration. The compounds of formula (I) may be compounded, for example with a pharmaceutically acceptable carrier for solid compositions such as tablets, pellets or capsules; capsules containing liquids; suppositories; solutions; emulsions; suspensions or any other form suitable for use. Suitable carriers include, for example, sterile water, sterile physiological saline, gum acacia, gelatin, starch paste, talc, keratin, colloidal silica, urea and the like. In addition, auxiliary, stabilizing, thickening, lubricating and coloring agents may be used. The compounds of formula (I) are present in the compositions in an amount sufficient to inhibit AChE, and produce a desired effect upon Alzheimer's dementia, myasthenia gravis, an age-related memory impairment, Down's syndrome and glaucoma.

The compositions of this invention may be administered in a therapeutically effective amount by a variety of methods including orally, intramuscularly, intravenously, subcutaneously, transdermally, rectally or by inhalation. While the preferred mode of administration is through the oral mode, the precise mode of administration is left to the discretion of the practitioner. They are advantageously effective when administered orally.

Compositions for oral administration may be in the form of tablets, troches, lozenges, aqueous or oily suspensions, granules or powders, emulsions, capsules, syrups or elixirs. Orally administered compositions may contain one or more agents, such as, sweetening agents such as fructose, aspartame or saccharin, flavoring agents such as peppermint, oil of wintergreen, or cherry, coloring agents and

preserving agents, to provide a pharmaceutically palatable preparation. In the case of tablets, carriers which are commonly used include lactose, mannitol and corn starch; and lubricating agents, such as magnesium stearate, are commonly added. Moreover, compositions in tablet form may be coated to delay disintegration and absorption in the gastrointestinal tract thereby providing a sustained action over an extended period of time.

For oral administration in capsule form, the compound of formula (I) can be administered in dry form in a hard gelatin capsule or in a suitable gelled or liquid vehicle, such as a liquid polyethylene glycol or a carrageenan gel, in a soft gelatin capsule. Selectively permeable membranes surrounding an osmotically active driving compound are also suitable orally administered compositions.

In these later platforms, fluid from the environment surrounding the capsule is imbibed by the driving compound, which swells to displace the agent or agent composition through an aperture. These delivery platforms can provide an essentially zero order delivery profile as opposed to the spiked profiles of immediate release formulations. A time delay material such as glycerol monostearate or glycerol stearate may also be used.

Aqueous suspensions containing the compounds of formula (I) can be combined with emulsifying and suspending agents. Aqueous suspensions may also contain one or more preservatives, such as, for example, ethyl or n-propyl-p- hydroxybenzoate, one or more coloring agents, flavoring agents or sweetening agents.

For intramuscular, intraperitoneal, subcutaneous and intravenous use, sterile solutions of the compound of formula (I), preferably a pharmaceutically acceptable salt thereof, are usually prepared, and the pH of the solutions should be suitably adjusted and buffered. For intravenous use, the total concentration of solutes should be controlled in order to render the preparations isotonic.

When a compound of formula (I) is used as in a mammal, preferably a human subject, the daily dosage will normally be determined by the prescribing physician with the dosage generally varying according to the age, weight, and response of the individual patient, as well as the severity of the patient's symptoms. However, in most instances, an effective daily dosage of the compound of formula (I) will be in the range of from about 0.05 mg/kg to about 1 mg/kg of body weight, and preferably, of from about 0.1 mg/kg to about 0.5 mg/kg of body weight, administered in single or divided doses. In a preferred embodiment, a 50 mg tablet comprising about 100 Ug of a compound of formula (I) is administered about 4 to about 8 times per day. In some cases, however, it may be necessary to use dosages outside these limits, depending, e.g., on the route and frequency of administration. Treatment can be repeated as needed, depending upon the dosage and need.

Furthermore, the compounds of formula (I) or pharmaceutically acceptable salts thereof can be used for research purposes, for example, to investigate the mechanism and activity of AChE inhibitors.

The following examples are set forth to assist in understanding the invention and should not, of course, be construed as specifically limiting the invention described and claimed herein. Such variations of the inventions which would be within the purview of those in the art, including the substitution of all equivalents now known or later developed, including changes in formulation or minor changes in experimental design, are to be considered to fall within the scope of the invention incorporated herein.

5. EXAMPLE: SYNTHESIS OF HUPERZINE A DERIVATIVES Example 1 O-Pivaloylhuperzine A. To 247 mg (1.02 mmol) of (-)-huperzine A, 0.71 mL (5.1 mmol) of triethylamine and 11.5 mg (0.1 mmol) of 4-(dimethylamino)pyridine in 8 mL of CH2Cl2 was added, with ice cooling, 126 ML (1.02 mmol) pivaloyl

chloride. The resulting mixture was allowed to stir for 5h, during which time the temperature of the reaction mixture was allowed to rise to room temperature. The reaction mixture was admixed with 1 g of ELITES, and the volatiles were evaporated therefrom. The resulting ELITES mixture was purified using silica gel chromatography with 1:1 ethyl acetate:hexane as an eluent to obtain 310 mg (93%) of the above-titled compound as a colorless oil which slowly solidified: 'H NMR (CDCl3, 300 MHz) 6 8.20 (d, 1H, J = 8 Hz), 6.85 (d, 1H, J = 8 Hz), 5.53 (q, 1H, J = 6.5 Hz), 5.43 (br d, 1H, J = 5 Hz), 3.68 (br, 1H), 3.04, 2.99 (ABq, 2H, J = 17 Hz, both parts d with J = 5.5 and 2 Hz, resp.), 2.20 (narrow ABq, 2H), 1.73 (d, 3H, J = 6.5 Hz), 1.56 (s, 3H), 1.51 (s, 2H), 1.37 (s, 9H); IR (KBr) 2972, 2929, 1754, 1657, 1580, 1450, 1239, 1113, 837 cm-!; MS (EI) m/z 326 (M+, 14%), 311, 241, 227, 213, 187, 57 (100%).

Example 2 O-(l-Adamantoyl)huperzine A. A solution of 12.4 mg (69 mol) of adamantane-l-carboxylic acid in 0.5 mL of SOCl2 was heated at reflux, with protection from moisture, for 2.3h. The excess SOCl2 was removed by evaporating, and the resulting residue was evaporated in the presence of benzene.

The crude acid chloride product was diluted with 0.3 mL of CH2Cl2, and the resulting solution was added, with ice cooling, to a solution of 15.0 mg (62 mol) of (-)-huperzine A, 42 uL (300 mol) of triethylamine, and 0.8 mg (6 mol) of 4-(dimethylamino)pyridine in 0.3 mL of CH2Cl2. The resulting mixture was allowed to stir at room temperature for 26h, and evaporated. The resulting residue was purified using silica gel chromatography with 1:2 ethyl acetate:hexane as an eluent to obtain 19.0 mg (76%) of the above-titled compound as a colorless glass: 'H NMR (CDCll, 300 MHz) 6 8.19 (d, lH, J = 8.5 Hz), 6.85 (d, 1H, J = 8.5 Hz), 5.52 (q, 1H, J = 6.5 Hz), 5.43 (br d, 1H, J = 5 Hz), 3.68 (br, 1H), 3.03, 2.95 (ABq, 2H, J = 17 Hz, both parts d with J = 5 and 2 Hz, resp.), 2.20

(narrow ABq, 2H), 2.07 (s, 9H), 1.75 (s, 6H), 1.73 (d, 3H, J = 6.5 Hz), 1.58 (s, 2H), 1.50 (s, 3H); '3C NMR (CDCl3, 75 MHz) 6 176.1, 156.6, 155.7, 143.0, 138.8, 137.4, 133.3, 125.1, 114.0, 111.4, 55.6, 50.9, 41.1, 40.3, 38.7, 36.5, 33.9, 27.9, 22.6, 12.6; IR (film) 2909, 2853, 1748, 1582, 1451, 1208, 1179, 1051, 754 cm'; MS (EI) m/z 404 (M+, 87%), 389, 376, 375, 361, 375, 361, 241, 227, 207, 135 (100%); HRMS (FAB) calc'd for C26H33N202 (M + H+) 405.2542, found 405.2540.

Example 3 O-Acyl Derivatives of Huperzine A. O-(o- Toluoyl)huperzine A, O-(2,4,6-trimethoxybenzoyl)huperzine A; O-(nicotinoyl)huperzine A; O-(O-acetylmandelyl)huperzine A and O-(isobutyryl)huperzine A are prepared according to the procedure of Example 1, above, except that o-toluoyl chloride, 2,4,6-trimethoxybenzoyl chloride, nicotinoyl chloride hydrochloride, O-acetylmandelic chloride and isobutyryl chloride respectively, are used in place of pivaloyl chloride.

Example 4 O-Acyl Derivatives of Huperzine A. O-(n- Caproyl)huperzine A, O-(n-Capryloyl)huperzine A, O-(n- Capryl)huperzine A, O-(n-Lauryl)huperzine A, O-(n- Myristyl)huperzine A, O-(n-Palmityl)huperzine A, O-(n- Stearyl)huperzine A, O-(Linoleyl)huperzine A, O- (Linolenyl)huperzine A, O-(Acetylsalicylyl)huperzine A, O- (2,2-dimethyl-3-phenylpropionyl)huperzine A, O-(1-methyl-1- cyclohexanecarbonyl)huperzine A and O-(endo-norbornane-2- carbonyl)huperzine A are prepared according to the procedure of Example 2, above, except that caproic acid, caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, linoleic acid, Ilnolenic acid, acetylsalicylic acid, 2,2-dimethyl-3-phenylpropionic acid (obtained, for example, from a Jones oxidation of 2,2-dimethyl-3-phenyl-l- propanol), l-methyl-l-cyclohexanecarboxylic acid and endo-

norbornane-2-carboxylic acid (obtained, for example, from the Diels-Alder reaction between 1,3-cyclopentadiene and acrylic acid, followed by hydrogenation), respectively, are used in place of adamantane-1-carboxylic acid.

Example 5 O-(tert-Butoxycarbonyl)huperzine A. To a mixture of 9.8 mg (40.4 Um) of (-)-huperzine A and 15 mg (0.12 mmol) of 4-(dimethylaminopyridine) was added a solution of 35 mg (0.16 mmol) of di-tert-butyl dicarbonate in 0.1 mL of anhydrous dichloromethane. Vigorous gas evolution instantaneously took place. The resulting mixture was allowed to stir at room temperature for 70 minutes, and then was filtered over silica gel using 1:6 ethyl acetate:hexane as a solvent. The fractions containing the above-titled product (Rj approx. 0.29) were evaporated and dried in vacuo to provide 11.0 mg (79%) of the above-titled product as a colorless film: 'H NMR (CDCls, 300 MHz) 6 7.91, 7.03 (d, 2H, J = 8.5 Hz), 5.71 (q, 1H, J = 7 Hz), 5.44 (br. d, 1H, J = 5 Hz), 3.71 (br., 1H), 3.07, 2.95 (ABq, 2H, J = 17 Hz, both parts d with J = 5 and 1.5 Hz, resp.), 2.69, 2.44 (ABq, 2H, J = 16.5 Hz, A part br.), 1.75 (d. 3H, J = 7 Hz), 1.60 (s, 2H, NH2), 1.55 (s, 9H), 1.53 (s, 3H); '3C NMR (CDCl3, 75 MHz) s 156.53, 154.66, 151.13, 137.26, 135.80, 135.57, 132.06, 124.99, 114.11, 113.86, 84.05, 63.01, 51.96, 39.62, 33.27, 27.68, 22.22, 12.46.

Example 6 O-(Cholinecarbonyl)Huperzine A. To 1 eq. of choline chloride and 1-2 eq. of poly(4-vinylpyridine) in dichloromethane is added between 1-2 eq. of phosgene at OOC.

The resulting mixture is allowed to stir at OOC for 20 min., whereupon 1 eq. of additional poly(4-vinylpyridine), followed by 1 eq. of huperzine A, are added. The resulting mixture is allowed to stir at 0°C for 2h, and then at room temperature for 20 min. The reaction mixture is filtered, concentrated in vivo, and crystallized from a polar solvent such as

methanol, or from a non-polar solvent such as benzene or hexane, to afford the above-titled product.

6. EXAMPLE: INHIBITION OF ACETYLCHOLINESTERASE This example illustrates the effectiveness of the compounds of formula (I) at inhibiting AChE.

A compound of formula (I) is incubated with excess AChE-free human plasma obtained according to the method of D.

De La Hoz et al., Life Sci. 39:195-99 (1986). The human plasma contains an esterase that converts the compound of formula (I) to huperzine A. An aliquot of the resulting incubation mixture is removed, and its ability to inhibit AChE is measured in 50 mM sodium phosphate containing 1 mM dithionitrobenzoic acid (pH 8.0) at 22 OC, according to the procedure of Ellman et al., Biochem. Pharmacol. 1:88-95 (1961), using 1 mM acetylthiocholine as the substrate.

Inhibition of AChE is achieved by diluting an appropriate volume of a stock solution of a compound of formula (I) (2-5 mM) into an enzyme solution (15-20 units of AChE/mL in 50 mM sodium phosphate (pH 8.0), containing 0.01% bovine serum albumen), and measuring residual enzyme activity at various times. Plots of percent residual activity vs. time at each concentration are used to calculate the rate of inhibition (k",). Direct measurement of the rate constant of regeneration of enzyme activity (koll) is initiated by a >10,000-fold dilution of huperzine A-inhibited AChE (2-4 M) to show that the rate of inhibition by residual initiator is negligible in the reactivation medium. The interaction of huperzine A ("HUP-A" in Scheme 1) with AChE ("E" in Scheme 1) can be described by Scheme 1, below: Scheme 1

The ratio "ko,f/ko"" is the dissociation constant (K,).

Alternatively, the K, values for the inhibition of fetal bovine serum AChE with huperzine A derived from the compound of formula (I) is determined by analysis of kinetic data described according to Scheme II, below: Scheme 2 where K, (the competitive inhibition constant) and a-K, (the uncompetitive inhibition constant) reflect the interaction of huperzine A with free AChE and the enzyme-substrate complex, respectively. "S" is the acetyl thiocholine substrate, and "P" is acetate and thiocholine product. Data for this analysis is obtained by measuring inhibition of enzyme activity over an acetylthiocholine concentration range of 0.025-0.4 mM and at a series of huperzine A concentrations.

Plots of reciprocal velocities vs. reciprocal substrate concentrations yield a family of slopes. Replots of slopes and intercepts vs. inhibitor concentrations are used for the determination of K, and aK, values, respectively.

This assay demonstrates that the compounds of formula (I), upon hydrolysis by a plasma esterase, show AChE inhibition that is comparable to that obtained with huperzine A when tested under analogous conditions, i.e., about 7 to about 45 nM for K,.

7. EXAMPLE: LACK OF INHIBITION OF BUTYRYLCHOLINESTERASE This example illustrates the ineffectiveness of the compounds of formula (I) at inhibiting butyrylcholinesterase ("BChE").

BChE obtained from horse serum (Sigma Chemical Company, St. Louis, Missouri) is purified according to the method of De La Hoz et al., Life Sci. 39:195-99 (1986). BChE activity is measured in 50 mM sodium phosphate containing lmM dithionitrobenzoic acid (pH 8.0) at 22 OC as described in Ellman et al., Biochem. Pharmacol. 1:88-95 (1961), using butyrylthiocholine as the substrate, and according to the protocol of Example 6, above.

The results of this assay show that neither Huperzine A nor the compounds of formula (I) inhibit BChE at concentrations greater than 5 mM. Therefore, unwanted side effects that accompany in vivo BChE inhibition, including nausea and dizziness, are absent from patients administered with the compounds of formula (I).

The present invention is not to be limited in scope by the specific embodiments disclosed in the examples which are intended as illustrations of a few aspects of the invention and any embodiments which are functionally equivalent are within the scope of this invention. Indeed, various modifications of the invention in addition to those shown and described herein will become apparent to those skilled in the art and are intended to fall within the appended claims.

A number of references have been cited and the entire disclosures of which are incorporated herein by reference.