Background of the Invention

Recent research in the fields of separation technology and pharmaceutical compounds reveals that many reactions between chemical compounds result from the three dimensional structure, and the molecular interactions between different compounds. A complementary structural relationship has been tied to a particular chemical compounds ability to react with a second chemical compound (see, for example, "The Concept of Molecular Structure in Structure-Activity Relationship Studies and Drug Design", Testa et al.. Medicinal Research Reviews, 1991, Vol. 11, No. 1) . The present invention relates to hydroxyethyl aminimide chemical structures which can be used as molecular scaffolding on which to hang different substituent groups. By varying the different substituent groups on an aminimide chemical backbone as disclosed herein it is possible to develop chemical compounds having a complementary structural and molecular relationship to a target compound, enzyme, molecular recognition site or receptor. Use of the present invention represents an improvement in both the cost and time efficiency of identifying lead compounds.

Hydroxyethyl aminimides (herein after referred to as aminimides) , can be prepared from the one-step reaction of an ester or acid chloride, a hydrazine, and an epoxide according to a method such as that disclosed by Middleton, United States Patent 3,963,776 and Culbertson, United States Patent 3,963,703. Alternatively, hydroxyethyl aminimides can be formed from the alkylation of a disubstituted hydrazide through the opening of an epoxide such as by the reactions disclosed in Grimm, United States Patent 3,850,969. An extensive discussion of aminimides including their preparation and uses is set forth in PCT application PCT/US93/12612 filed December 28, 1993 in the name of ArQule Partners, L.P. which is herein incorporated by reference in its entirety.

Aminimides have a diversity of properties and are known

to be useful as surfactants, (see, for example, Falk, United States Patent 4,102,916, and Middleton, United States Patent 3,963,776), resin hardeners, precursors to isocyanates (see, for example, Brutchen, United States Patent 3,898,087), in the formation of polyurethanes (see, for example, Kresta, United States Patent 4,067,830) and polyisocyanurates ( see Kresta, United States Patent 3,925,284).

Much less is known about the biological activity of aminimides. Kabara has shown that specific aliphatic derived dimethyl-hydroxyethyl aminimides possess antimicrobial (see United States Patents 4,189,481 and 4,217,364) and antifungal properties (see United States Patents 3,934,029 and 3,934,031). L. Boutis, et al . , have observed antineoplastic activity (Current Chemotherapy, 1978, 2 , 1213-1216), while M. Tichniouin, et al . demonstrated that certain dimethyl- hydroxyethyl aminimides possess a noticeable vasodilating activity (Eur. J . Med . Chem . , 1982, 17 , 265-270). Yet, to date, no one has used an aminimide moiety, and, in particular, a hydroxyethyl aminimide moiety as a peptide isostere in the design of pharmacologically active compounds.

The present invention relates to the use of hydroxyethyl aminimides as isosteres in the design and synthesis of chemical compounds capable of binding to an active site of a receptor or enzyme or to a molecular recognition site in, for example, separation chemistry.

Summary of the Invention It is an object of this invention to provide a novel class of hydroxyethyl aminimide compounds useful for their complementary properties to molecular recognition sites and/or enzymes.

Another object of this invention is to provide a method of making chemical compounds which are complementary to other chemical compounds. Other objects of this invention will be apparent to those skilled in the art to which this invention applies.

The objects of this can be accomplished using a chemical

backbone having the following chemical formula I:

a. structural diversity elements A, B, C, E, F and G are the same or different, and each is selected from the group consisting of a chemical bond; hydrogen; electrophilic group; a nucleophilic group; an amino acid derivative; a nucleotide derivative, a carbohydrate derivative; an organic structural motif; a reporter element; an organic moiety, optionally containing a polymerizable group; a macromolecular component, wherein the structural diversity elements A, B, C, E, F and G are optionally connected to each other or to other structures; D is a selected from the group consisting of hydrogen, branched or straight chain lower alkyl having from 1-8 carbon atoms, ether and ester groups, and wherein n is an integer greater than 0.

Detailed Description Of The Invention The present invention relates to the use of hydroxyethyl aminimides and to their use as molecular recognition agents in the design and synthesis of compounds for use as biologically active compounds and in separations technology.

A peptide isostere is a moiety that, when substituted for the peptide bond, will confer upon the analog certain stearic and/or electronic configurations similar to the parent compound, thereby allowing the analog to possess biological properties similar to the parent compound. However, the isostere is designed to be resistant to degradation by the same pathways as a nominal peptide.

For the purposes of the present invention, the term complementary is given that definition currently used in the chemical and biochemical arts that refers to a close three

dimensional and/or molecular interaction relationship between two different compounds.

The term "backbone" is defined, for the purpose of the present invention, as an organic chain of elements that can be substituted with one or more structural diversity elements to yield a chemical compound or a class of chemical compounds which are complementary to a second chemical compound or class of chemical compounds.

The hydroxyethyl aminimides of the present invention have a chemical backbone with the following chemical formula I:

a. structural diversity elements A, B, C, E, F and G are the same or different, and each is selected from the group consisting of a chemical bond; hydrogen; electrophilic group; a nucleophilic group; an amino acid derivative; a nucleotide derivative, a carbohydrate derivative; an organic structural motif; a reporter element; an organic moiety, optionally containing a polymerizable group; a macromolecular component, wherein the structural diversity elements A, B, C, E, F and G are optionally connected to each other or to other structures, D is a selected from the group consisting of hydrogen, branched or straight chain lower alkyl having from 1-8 carbon atoms, ether and ester groups, and n is an integer greater than 0. For this invention, it is understood that each integer that n can be, represents a structural embodiment of the backbones of this invention. Thus each integer from 1 to at least about 100,000 to 500,000 is expressly disclosed as preferred embodiments of the present invention. Higher values of n can be used, if desired, for specialty polymers.

The particular structural diversity elements can vary greatly, depending upon the specific compound to be prepared.

One of ordinary skill in the chemical arts is well aware of the bonding properties, and capabilities, of these elements, and can easily select the appropriate element for attachment to the particular location on the backbone. Thus, the backbone represents a very valuable tool for constructing any one of a wide variety of compounds, and it represents an essential feature of this invention.

The synthesis and design of aminimide compounds is well known in the art and is detailed for example in PCT/US93/12612 referenced above. The aminimide compound of the present invention can be synthesized in a similar manner by many routes. It is well known in the art of organic synthesis that many different synthetic protocols can be used to prepare a given compound. Different routes can involve more or less expensive reagents, easier or more difficult separation or purification procedures, straightforward or cumbersome scale- up, and higher or lower yield. The skilled synthetic organic chemist knows well how to balance the competing characteristics of synthetic strategies. Thus the compounds of the present invention are not limited by the choice of synthetic strategy, and any synthetic strategy that yields the compounds described above can be used.

Accordingly, any known method of producing the subject hydroxyethyl aminimide compounds can be to produce a wide variety of chiral aminimide conjugates of the following general structures:

The structural diversity elements A, B, C, E, F and G may be the same or different, may be of a variety of structures and may differ markedly in their physical or functional properties, or may be the same; they may also be chiral or symmetric. The structural diversity elements A, B, C, E, F and G are preferably selected from:

1) amino acid derivatives of the form (AA) _n , which would include, for example, natural and synthetic amino acid residues (n = 1) including all of the naturally occurring alpha amino acids, especially alanine, arginine, asparagine, aspartic acid, cysteine, glutamine, glutamic acid, glycine, histidine, isoleucine, leucine, lysine, methionine, phenylalanine, proline, serine, threonine, tryptophan, tyrosine; the naturally occurring disubstituted amino acids, such as amino isobutyric acid, and isovaline, etc.; a variety of synthetic amino acid residues, including alpha- disubstituted variants, species with olefinic substitution at the alpha position, species having derivatives, variants or mimetics of the naturally occurring side chains; N-substituted glycine residues; natural and synthetic species known to functionally mimic amino acid residues, such as statine, bestatin, etc. Peptides (n = 2 - 30) constructed from the amino acids listed above, such as angiotensinogen and its family of physiologically important angiotensin hydrolysis products, as well as derivatives, variants and mimetics made from various combinations and permutations of all the natural and synthetic residues listed above. Polypeptides (n = 31 - 70) , such as big endothelin, pancreastatin, human growth hormone releasing factor and human pancreatic polypeptide. Proteins (n > 70) including structural proteins such as collagen, functional proteins such as hemoglobin, regulatory proteins such as the dopamine and thrombin receptors. Depsipeptides which include a derivatives of amino acids, peptides, polypeptides and proteins that contain a hydroxy and amino acid residual linked by amide or ester bonds, and include peptide-related compounds such as azinothricin, actinomycin, and echinomycin.

2) a nucleotide derivative of the form (NUCL) _n , which includes natural and synthetic nucleotides (n = 1) , such as adenosine, thymine, guanidine, undine, cytosine, derivatives of these and a variety of variants and mimetics of the purine ring, the sugar ring, the phosphate linkage and combinations of some or all of these. Nucleotide probes (n = 2 - 25) and oligonucleotides (n > 25) including all of the various possible; homo and hetero-synthetic combinations and permutations of the naturally occurring nucleotides; derivatives and variants containing synthetic purine or pyrimidine species, or mimics of these; various sugar ring mimetics; and a wide variety of alternate backbone analogs, including but not limited to phosphodiester, phosphorothionate, phosphorodithionate, phosphoramidate, alkyl phosphotriester, sulfamate, 3 '-thioforimacetal, methylene

(methylimino) , 3-N-carbamate, morpholino carbamate and peptide nucleic acid analogs.

3) a carbohydrate derivative of the form (CH)„, which would include natural physiologically active carbohydrates; related compounds, such as glucose, galactose, sialic acids, /3-D-glucosylamine and nojorimycin, which are both inhibitors of glucosidase; pseudo sugars, such as 5α-carba-2-D- galactopyranose, which is known to inhibit the growth of Klebsiella pneumonia (n = 1) ; synthetic carbohydrate residues and derivatives of these (n = 1) and all of the complex oligomeric permutations of these as found in nature, including high mannose oligosaccharides, the known antibiotic streptomycin (n > 1) .

4) a naturally occurring or synthetic organic structural motif. The term 'motif is defined as an organic molecule having or containing a specific structure that has molecular recognition characteristics, such as a molecule having a complementary structure to an enzyme active site, for example. This term includes any of the well known basic structures of pharmaceutical compounds including pharmacophores, or metabolites thereof. These basic structures include beta-lacta s, such as penicillin, known to

inhibit bacterial cell wall biosynthesis; dibenzazepines, known to bind to CNS receptors and used as antidepressants; polypeptide macrolides, known to bind to bacterial ribosymes, etc. These structural motifs are generally known to have specific desirable binding properties to ligand acceptors.

5) a reporter element, such as a natural or synthetic dye or a residue capable of photographic amplification which possesses reactive groups that may be synthetically incorporated into the aminimide structure or reaction scheme, and may be attached through the groups without adversely interfering or affecting with the reporting functionality of the group. Preferred reactive groups are amino, thio, hydroxy, carboxylic acid, carboxylic acid ester, particularly methyl ester, acid chloride, isocyanate alkyl halides, aryl halides and oxirane groups.

6) an organic moiety containing a polymerizable group such as a double bond, or other functionalities capable of undergoing condensation polymerization or copolymerization. Suitable groups include vinyl groups, oxirane group, carboxylic acids, acid chlorides, esters, amides, azlactones, lactones and lactams. Other organic moieties may also be used.

7) a macromolecular component, such as a macromolecular surface or structures which may be attached to the aminimide modules via the various reactive groups outlined above, in a manner where the binding of the attached species to a ligand-receptor molecule is not adversely affected and the interactive activity of the attached functionality is determined or limited by the macromolecule. Examples of macromolecular components include porous and non-porous inorganic components, such as, for example, silica, alumina, zirconia, titania and the like, as commonly used for various applications, such as normal and reverse phase chromatographic separations, water purification, pigments for paints, etc. ; porous and non-porous organic macromolecular components, including synthetic components such as styrene-divinyl benzene beads, various methacr late beads, PVA beads, and, the like,

commonly used for protein purification, water softening; and a variety of other applications, natural components such as native and functionalized celluloses, such as, for example, agarose and chitin, sheet and hollow fiber membranes made from nylon, polyether sulfone or any of the materials mentioned above. The molecular weight of these macromolecules may range from about 1000 Daltons to as high as possible. They may take the form of nano-particles (dp = 100 - 1000 Angstroms) , latex particles (dp = 1000 - 5000 Angstroms) , porous or non-porous beads (dp = 0.5 - 1000 microns), membranes, gels, macroscopic surfaces or functionalized or coated versions or composites.

The structural diversity elements A, B, C, E, F and G may also be a chemical bond to a suitable organic moiety, a hydrogen atom, an organic moiety which contains a suitable electrophilic group, such as an aldehyde, ester, alkyl halide, ketone, nitrile, epoxide or the like; a suitable nucleophilic group, such as a hydroxyl, amino, carboxylate, amide, carbanion, urea or the like; or one of the structural diversity elements C and/or D groups defined below. In addition, structural diversity elements A, B, C, D, E, F and/or G may join to form a ring, bi-cyclic or tri-cyclic ring system; or structure which connects to the ends of the repeating unit of the compound defined by the preceding formula; or may be separately connected to other moieties. A more generalized structure of the composition of this invention can be represented by the following structural formulas:

wherein: a. at least one of the structural diversity elements A, B, C, E, F and G are as defined above and are optionally connected to each other or to other bonds and/or may each represent a chemical bond or one or more atoms of carbon, nitrogen, sulfur, oxygen, phosphorus, silicon or combinations thereof; b. structural diversity elements A, B, C, E, F and G are the same or different and each represents A, B, E, cyano, nitro, halogen, oxygen, hydroxy, alkoxy, thio, straight or branched chain alkyl, carbocyclic aryl and substituted or heterocyclic derivatives thereof, wherein structural diversity elements E and F may be different in adjacent n units and have a selected stereochemical arrangement about the carbon atom to which they are attached.

As used herein, the phrase linear chain or branched chained alkyl groups means any substituted or unsubstituted acyclic carbon-containing compounds, including alkanes, alkenes and alkynes. Alkyl groups having up to 30 carbon atoms are preferred. Examples of alkyl groups include lower alkyl, for example, methyl, ethyl, n-propyl, iso-propyl, n-butyl, iso-butyl or tert-butyl; upper alkyl, for example, octyl, nonyl, decyl, and the like; lower alkylene, for example, ethylene, propylene, propyldiene, butylene, butyldiene; upper alkenyl such as 1-decene, 1-nonene, 2,6-dimethyl-5-octenyl, 6-ethyl-5-octenyl or heptenyl, and the like; alkynyl such as 1-ethynyl, 2-butynyl, 1-pentynyl and the like. The ordinary skilled artisan is familiar with numerous linear and branched alkyl groups, which are within the scope of the present invention.

In addition, such alkyl group may also contain various substituents in which one or more hydrogen atoms has been replaced by a functional group. Functional groups include but are not limited to hydroxyl, amino, carboxyl, amide, ester, ether, and halogen (fluorine, chlorine, bromine and iodine) , to mention but a few. Specific substituted alkyl groups can be, for example, alkoxy such as methoxy, ethoxy, butoxy, pentoxy and the like, polyhydroxy such as 1,2-dihydroxypropyl, 1,4-dihydroxy-l-butyl, and the like; methyla ino, ethylamino, dimethylamino, diethylamino, triethylamino, cyclopentylamino, benzylamino, dibenzylamino, and the like; propionic, butanoic or pentanoic acid groups, and the like; formamido, acetamido, butanamido, and the like, methoxycarbony1, ethoxycarbonyl or the like, chloroformyl, bromoformyl, 1,1-chloroethyl, bromoethyl, and the like, or dimethyl or diethyl ether groups or the like.

As used herein, substituted and unsubstituted carbocyclic groups of up to about 20 carbon atoms means cyclic carbon- containing compounds, including but not limited to cyclopentyl, cyclohexyl, cycloheptyl, adamantyl, and the like. Such cyclic groups may also contain various substituents in which one or more hydrogen atoms has been replaced by a functional group. Such functional groups include those described above, and lower alkyl groups as described above. The cyclic groups of the invention may further comprise a hetero-atom. For example, in a specific embodiment, structural diversity element A is cyclohexanol.

As used herein, substituted and unsubstituted aryl groups means a hydrocarbon ring bearing a system of conjugated double bonds, usually comprising (4p - 2) pi bond electrons, where p is an integer equal to or greater than 1. Examples of aryl groups include, but are not limited to, phenyl, naphthyl, anisyl, toluyl, xylenyl and the like. According to the present invention, aryl also includes aryloxy, aralkyl, aralkyloxy and heteroaryl groups, e.g., pyrimidine, morpholine, piperazinc, piperidine, benzoic acid, toluene or thiophene and the like. These aryl groups may also be

substituted with any number of a variety of functional groups. In addition to the functional groups described above in connection with substituted alkyl groups and carbocyclic groups, functional groups on the aryl groups can be nitro groups.

As mentioned above, structural diversity elements can also represent any combination of alkyl, carbocyclic or aryl groups; for example, 1-cyclohexylpropyl, benzylcyclohexylmethyl, 2-cyclohexyl-propyl 2,2- methylcyclohexylpropyl, 2,2-methylphenylpropyl, 2,2 methylphenybutyl, and the like.

C. A and G may be a chemical bond or a connecting group that includes a terminal carbon atom for attachment to the quaternary nitrogen and G may be different in adjacent n units; and d. n is an integer greater than 0.

In one embodiment of the invention, at least one of A, B, C, D, E, F and G represents, an organic or inorganic macromolecular surface. Examples of preferred macromolecular surfaces include ceramics such as silica and alumina, porous and non-porous beads, polymers such as a latex in the form of beads, membranes, gels, macroscopic surfaces or coated versions or composites or hybrids thereof. This functionalized surface may be represented as follows.

In a further embodiment of the invention, the above roles of diversity elements A and E are reversed, so that E is the substituent selected from the foregoing list and A represents a functionalized surface, as shown below.

In a further embodiment of the invention, the above roles of diversity elements A and B are reversed, so that A is the substituent selected from the foregoing list and B represents a functionalized surface, as shown below.

In a third preferred embodiment of the invention, either diversity elements A, B, E, two, three or all four contain one or more double bonds capable of undergoing free-radical polymerization or co-polymerization to produce achiral or chiral oligomers, polymers, copoly ers, etc.

From the preceding, it is seen that the skilled artisan can design a particular compound in an attempt to achieve a desired goal. In the area of pharmaceuticals, for example, the backbone can be used as a starting point for attachment of a wide variety of diversity elements. The pharmacological activity of the resulting compounds can be easily and accurately screened, since the final structure of the compound is predictable and highly controlled. Methods of screening or testing hydroxyethyl aminimide compounds for their reactivity and/or complementary nature with respect to a second chemical compound or class of compounds or enzyme, molecular recognition structure receptor is detailed in U.S. Patent application 08/248,263 by Joseph C. Hogan, filed May 23, 1994, the entire content of which is specifically incorporated by reference herein.

The human immunodeficiency virus (HIV) has been implicated as the causative agent of acquired immune deficiency syndrome (AIDS) (see Popovic; et at . , Science, 1984, 198 , 497). The RNA genome of the HIV retrovirus encodes an aspartic protease known as the HIV-1 protease (see Kramer, H. A.; et al . , Science, 1986, 231 , 1580). This protease is required for malitration and proliferation of the infectious virion. The role of the HIV-l protease is to cleave, viral precursor proteins, in particular the Gag and Pol precursor proteins, into, their active forms (see Darke, P. L. ; et al . , Biochem . Biophys . Res . Comm . , 1988, 156 , 297) . The HIV-l protease is formed by the homodimerization of a 99 amino acid polypeptide; the active site of the protease is at the interface of the two subunits, with each subunit contributing one of the essential aspartic acid residues required for catalysis. The X-ray crystal structure of the HIV-l protease has been solved and shows that the dirtier structure is of C ₂ symmetry in its unbound form (see Navia, M. A.; et al . , Nature, 1989, 337, 615). The structure clearly illustrates the extended active site of the protein, which incorporates processing site of S4-S3' (using the subsite nomenclature of Schechter and Berger, Biochem . Biophys . Res . Comm . , 1967, 27 , 157) . Independent substrate cleavage assays have indicated that substrate specificity of HIV-l protease is significantly determined by subsites S2-S2' (see Pettit, S. C. ; et al . , Persp. in Drug Disc . Deε . 1993, 2, 69).

To date, numerous inhibitors of HIV-l protease have been reported in the literature (see, for instance, Wlodawer, A. ; Erickson, J. W., Annu. .Rev. Biochem . , 1993, 62 , 543). In certain examples, co-crystal structures of the protein/inhibitor complex have been solved, for example see C. L. Waller et al., J . Med . Chem . , 1993, 36 , 4152-4160, allowing researchers to better understand the structure/activity relationships of the active inhibitors. Approaches towards structure-based inhibitor design have taken three routes: 1. transition-state analog inhibitors (see Grobelny, D. ; et al . , Biochem . Biophys . Res . Comm . , 1990, 169 , llll) ; 2. substrate

analog inhibitors (see Moore, M. L. ; Dreyer, G. B, Persp. in Drug Disc . Des . 1993, 1, 85); and, 3. de novo designed inhibitors (see Lam, P. Y. S.; et al . , Science , 1994, 263 , 380) . In the design of transition-state analogues, researchers have attempted to replace the scissile amide bond with a non-hydrolyzable peptide isostere. A selection of successful inhibitor designs is illustrated in Figure l. Some of the more potent inhibitors of HIV-l protease reported are shown in Figure 2.

Normal Peptide

Hydroxyethylamine Reduced Amide

Hydroxycthylene

Dihydroxyethylene Phosphinatβ

Figure 1: Examples of transition-state isosteres employed as inhibitors of proteases.

U- ^β 4654 ^ββ , < 1 nM

Ro-31-8S8£ K _j . OJ nM

Figure 2: Previous Inhibitors of HIV-l protease.

This invention discloses a novel transition-state analog inhibitor structure, which is an effective antagonist of the HIV-l protease. In this peptide isostere, the scissile amide bond has been replaced with an aminimide linkage as illustrated in Figure 3. Among the advantages of using an aminimide isostere are their ease of syntheses, and the ability to modify the target structures in a modular fashion by varying either the epoxide, hydrazine, or ester components used in the syntheses of new compounds. Furthermore, the aminimide moiety confers an increase water solubility of the synthesized compounds.

Aminimide

Figure 3: Structure of an aminimide isostere.

Our prospective inhibitor I was designed using a model based on data from previous inhibition studies with HIV-l protease. Compound I was modeled in the active-site of HIV-l protease using the crystallographic data of the protein complexed with the inhibitor U-855488e (Brookhaven PDB identification code 8HVP) . Energy refinements of the inhibitor in the presence of the fixed protein and in vacuo showed that no large conformational changes in the inhibitor were required in order to adopt the bound conformation.

Examples

In order to exemplify the results achieved using the chemical backbone of the present invention, the following examples are provided without any intent to limit the scope of the instant invention to the discussion therein, all parts are by weight unless otherwise indicated.

Example 1 The following is one example of the utility of a hydroxyethyl aminimide moiety being used as a motif for the design of complementary molecular structures.

Experimental: Synthesis

Synthesis of compound I required the three building blocks for the aminimide: 1. The enantiomerically pure t-butoxycarbony1 (t-BOC) protected epoxide (1) , derived from phenylalanine; 2. the benzyl methyl hydrazine (2) and 3. methyl benzoate (3) .

phenylalanine; 2. the benzyl methyl hydrazine (2) and 3 methyl be

Compound I

Synthetic route 1

2

The synthesis of compound I is depicted in Scheme 1. To an isopropanol solution of 1.43 mmol of a chiral epoxide 1 (prepared using the method of Luly, et al . , J . Org . Chem . , 1987, 52 , 1487) and 1.43 mmol of hydrazine 2 (synthesized from the procedure of Ohme, R. ; Preuschof, H. , J . Pract . Chem . , 1970, 312 , 349) is added 1.43 mmol of the commercially available methyl ester 3. The reaction is stirred at 60 °C for 5 h. HPLC analysis of the crude reaction indicated the presence of two diastereo ers, which is expected due to the fixed chirality of the hydroxyethyl component and the resulting quaternary nitrogen of compound I. The solvent is removed under reduced pressure, and the crude oil is partially purified via silica gel column chromatography. A sample for enzymological testing is acquired by further purifying the isolated material by recrystallization to afford a white, crystalline solid product. The product is shown to be the desired compound I by H ¹ NMR and mass spectroscopy. HPLC analysis of the product indicates that isomer (a) of compound I is obtained free of isomer (b) after column chromatography and repeated crystallization.

Experimental: Enzymology

The inhibition constant (K _; ) of compound la is determined using HIV-l protease kit supplied by NovaBiochem (cat. #10-39- 0001, which supplies a solid phase synthesized analog of the protease, incorporating the unnatural residue aminobutyric acid in place of both cysteine residues 67 and 95, along with a thioester linkage in place of the normal peptide bond between residues 51-52) . A fluorometric assay is performed using a fluorogenic substrate supplied by NovaBiochem (cat. #05-23-5216, Abz-Thr-Ile-Nle-Phe(N0 ₂ )-Gln-Arg-NH ₂ ) . Initial rates of substrate hydrolysis are determined by following the increase in the fluorescence emission at 420 nm (excitation is at 325 nm) as the substrate is digested by the protease. The initial rates of substrate cleavage is determined in the absence and presence of compound la (up to a concentration of la = 500 nM) . A Lineweaver-Burk analysis of la indicates that inhibition follows classical competitive inhibition (Figure 4) . Replotting the slopes from the Lineweaver-Burk plot (Figure 5) gives a calculated K ₍ value of 137 nM.

Lineweaver-Burk Plot for Compound I

1/[Substrate] (1/μM)

Figure 4 A Lineweaver-Burk analysis of compound la .

Ki Determination for Compound I

B βlOpβ

-200 - 100 100 200 300 400 500 600

PI nM

Figure 5: A Replot of the slopes obtained Lineweaver-Burk plot for compound la.

Given the potency of this inhibitor for HIV-l protease, the model of the bound complex was used to rationalize structure-activity relationships for a variety of substituents and to propose additional compounds for synthesis and evaluation. In particular, fragments from all three components of the inhibitor (the epoxide, the ester and the hydrazine) were evaluated as to the most feasible ways to maximize both hydrophobic and hydrogen bonding interactions complementary with the protein.

The scope of the following claims is intended to encompass all obvious changes in the elements, details, materials and arrangement of parts that will occur to one of ordinary skill in the art: