"Prostaglandin pharmaceutical compositions "

*****

Field of the invention This invention relates to the field of new compounds that are derivatives of prostaglandins whose main biological activity is in the treatment of glaucoma and ocular hypertension.

Glaucoma is a group of diseases of the optic nerve involving loss of retinal ganglion cells in a characteristic pattern of optic neuropathy. Although raised intraocular pressure (IOP) is a significant risk factor for developing glaucoma, there is no set threshold for intraocular pressure that causes glaucoma, a disease that leads to progressive, irreversible loss of vision.

Glaucoma affects 1 in 200 people aged 50 or younger and 1 in 10 over the age of 80: almost 3 million people in the United States and almost 14 million people worldwide have glaucoma, this is the third leading cause of blindness worldwide.

Glaucoma occurs when an imbalance in production and drainage of fluid in the eye (aqueous humour) increases eye pressure to unhealthy levels. It is known that elevated IOP can be, at least

partially, controlled by administering drugs which either reduce the production of aqueous humour within the eye or increase the fluid drainage, such as β-blockers, α-agonists, cholinergic agents, carbonic anhydrase inhibitors or prostaglandin analogs.

However, several side effects are associated with the drugs conventionally used to treat glaucoma. Topical β-blockers show serious pulmonary side effects, depression, fatigue, confusion, impotence, hair loss, heart failure and bradycardia.

Topical α-agonists have a fairly high incidence of allergic or toxic reactions; topical cholinergic agents (miotics) can cause visual side effects. The side effects associated with oral carbonic anhydrase inhibitors include fatigue, anorexia, depression, paresthesias and serum electrolyte abnormalities (The Merck Manual of Diagnosis and Therapy, Eighteenth Edition, M. H. Beers and R. Porter Editors, Sec. 9, Ch. 103} . The topical prostaglandin analogs (bimatoprost , latanoprost, travoprost and unoprostone) used in the treatment of glaucoma, can produce ocular side effects, such as increased pigmentation of the iris, ocular irritation, conjunctival hyperaemia, iritis,

uveitis and macular oedema {Martindale, Thirty- third edition, p. 1445) .

U.S. Patent No. 6,417,228 discloses 13-aza prostaglandins having functional PGF2α receptor agonist activity and their use in treating glaucoma and ocular hypertension.

The application No. WO 90/02553 discloses the use of prostaglandins PGA, PGB, PGE and PGF derivatives, in which the omega chain contains a ring structure for the treatment of glaucoma or ocular hypertension .

It has been also reported (Osborne N.N. et al . Inv. Opthalm & Visual Science 43, 1456-1464, 2002) that the ideal anti-glaucoma drug for the future may be an agent that not only reduces IOP but also possesses neuro-protective (versus retina ganglion cells) and vaso-protective (versus optic nerve head) properties .

It was found that the new compounds object of the present invention possess all these characteristics .

It has been also reported {Hoyng PF, et al . "Topical prostaglandins inhibit trauma-induced inflammation in the rabbit eye". Invest Ophthalmol

Vis Sci. 1986 Aug;27 (8) : 1217-25.) that pre-treatment with PGEl and PGF2α led to a lower rise in the aqueous prostaglandin E2 (PGE2) concentration and a reduced inflammatory response after corneal puncture. It has been suggested that PGEl and PGF2α reduced the trauma-induced inflammatory response by decreasing the formation of endogenous prostaglandins, as well as reflected by their concentration in aqueous humour. Nevertheless the use of PGEl and PGF 2α remains problematic due to their tolerability and side effects. Moreover it remains the need to increase the clinical activity reducing the intraocular pressure of the patients. Summary of the invention

Object of the present invention are new derivatives of prostaglandins that release H ₂ S able not only to eliminate or at least reduce the side effects associated with these compounds, but also to possess an improved pharmacological activity.

It has been surprisingly found that prostaglandin H ₂ S donating derivatives have a significantly improved overall profile as compared to parent prostaglandins both in terms of wider

pharmacological activity and enhanced tolerability .

In particular, it has been found that the prostaglandin H ₂ S donating derivatives, object of the present invention, can be employed for treating glaucoma and ocular hypertension. The compounds of the present invention are indicated for the reduction of intraocular pressure in patients either with open- angle glaucoma or with chronic angle-closure glaucoma, who underwent peripheral iridotomy or laser iridoplasty.

This invention also relates to processes for preparing these compounds and to pharmaceutical compositions containing these compounds.

In particular the polysulfurated groups, contained in the compounds object of the present invention, linked to the prostaglandins are polysulfurated groups containing 2 or more atoms of sulphur selected from the group comprising organic thiosulfonates or dithiole-thione derivatives such as (5- (p-hydroxyphenyl) -3H-1 , 2-dithiol-3-thione, or

1, 3-dithiol-2-thione-5-carboxylic acid, 3-thioxo-3H- 1, 2-dithiol-5-carboxylic acid, 3-thioxo-3H-l , 2- dithiole-4-carboxylic acid. Detailed description of the invention

Object of the present invention are prostaglandin H ₂ S donating derivatives of general formula (I) :

A-Y-W (I) wherein

A is a residue of prostaglandins or their derivatives of formula (II) :

(ID

B is -(CH ₂ ) _m -CH ₃ , m is 1-5; or

Vi and V ₂ , the same or different to each other, are zero or H; the bond can be a single bond when Vi and/or V ₂ are H or a double bond;

Y is zero; - (C _n . ) alkyl- , ~ (C _n - ) alkyl-CO- , -O-

(Cn _' )alkyl-O-, -OOC- (C _n - ) alkyl-COO- ; -O- (C _n - ) alkyl- , -HN- (C _n - )alkyl-, -OOC- (C _n - ) alkyl- ; - (C _n - ) alkyl -O-CO- (C _n -.) alkyl-; - (C _n - ) alkyl -CO-O- (C _n - -) alkyl- wherein (C _n .) alkyl and (C _n --) alkyl are straight or branched, and n' and n' ' , the same or different to each other, are 0-10;

W is a polysulfurated group containing 2 or more atoms of sulphur, selected from the group comprising an organic thiosulfonate moiety or a dithiole-thione derivative: more in particular, as a further preferred embodiment, W is an organic thiosulfonate moiety having formula (III) :

-S-SO ₂ -R (III) wherein -S-SO ₂ -R is linked to A-Y-; R is a straight or branched alkyl , such as methyl , ethyl , propyl ; alkenyl, alkinyl; alkylaryl, alkenylaryl, alkinylaryl; arylalkyl, arylalkenyl, arylalkinyl ; or cycloalkyl , cycloalkenyl , cycloalkinyl ; or aromatic and/or heterocyclic ring, all substituted or unsubstituted; or more in particular, as a further preferred embodiment, W is a dithiole-thione derivative having the following formula (IV) :

wherein Z is S (sulphur) and at least 1 Z is C=S (thione) and T is: -00C- ; or

wherein

Rl is H; -COOH; -NH ₂ ; -OH; -SH;

R2 is hydrogen,- -COOH; alkyl, alkenyl, alkynyl ; aryl ; fluoro, chloro, bromo; hydroxyl , alkyloxy, alkenyloxy, aryloxy, acyloxy; amino, alkylamino, arylamino; thio; cyano; nitro; acyl ; amido; and a 5 or 6-membered aromatic or non-aromatic ring containing 0, 1, or 2 heteroatoms selected from nitrogen, oxygen, or sulphur; pharmaceutically acceptable salts and stereoisomers thereof .

As a further preferred embodiment of the compounds of general formula (I) of the present

invention (CJalkyl, (C _n - ) alky1 and (C _n" ) alky1 are

(CH ₂ ) πA / (CH ₂ ) πA' , (CH ₂ ) nA _" respectively, wherein nA, nA' and nA' ' , the same or different to each other, are 1-10, such as that more preferably Y is selected from the group comprising -(CH ₂ J _n A--, ~ (CH ₂ ) ^- -CO- ,

~0- (CH ₂ ) _HA - -O- , -0OC-(CH ₂ ) _nA --C00-; -O- (CH ₂ ) ,*.-, -HN-

(CH ₂ ) _πA --, -OOC- (CH ₂ ) _πA --; - (CH ₂ ) ^- -0-C0- (CH ₂ ) ^..-;

- (CU ₂ ) nA _' -CO-O- (CH ₂ ) nA _" - wherein nA, nA' and nA' ' , the same or different to each other, are 1-10. A further preferred embodiment of the prostaglandin derivative compounds according to the present invention are the compounds of general formula (I) wherein the group -Y-W is selected from the group comprising thiosulfonate moieties derived from the corresponding precursors having formula: S- (2-carboxyethyl) methanthiosulfonate, S- (2- aminoethyl) methanthiosulfonate and S- (2-hydroxyethyl) methanthiosulfonate .

A further preferred embodiment of the prostaglandin derivative compounds according to the present invention, are the compounds of general formula (I) wherein the polysulfurated group W is selected from the group comprising dithiole-thione derivatives of the corresponding precursors having

formula: 5- (p-hydroxyphenyl) -3H-1, 2-dithiol-3-thione, 1 , 3-dithiol-2-thione-5-carboxylic acid, 3-thioxo-3H- 1 , 2-dithiole-5-carboxylic acid, 3-thioxo-3H-l, 2- dithiole-4-carboxylic acid. In the present invention the parent compound is considered in its original form or in a proper modification to allow the chemical manipulation with the moiety containing the polysulfurated group.

The prostaglandin or its derivatives, such as the analogs bimatoprost, latanoprost, travoprost and unoprostone, and the moiety containing the polysulfurated group can be linked via different linking groups such as esters, amides, imides, sulfonamides, azo groups, carbamates, carbonates, anhydrides, acetals, thioacetals, etc. The polysulfurated group, i.e. the thiosulfonate moiety or dithiol-thionic derivative, can be also directly linked by an ionic bond to the prostaglandin as salt when Y=O. Bi-functional linkers (Y) , known to the expert in the field, (such as ethyl, propyl, or butyl diols; di-amines; hydroxy amines; etc.) can be optionally present when they are necessary to link the drug

(prostaglandin) to the polysulfurated group.

As a further object of the present invention are the preferred compounds according to general formula (I) , such as :

(Hoc, 13B, 15S) -11, 15-dihydroxy-9-oxoprost-13-en-l-oic acid 4- (3H-1 , 2-dithiole-3-thione-5-yl) -phenyl ester

(5Z) -7- [ (1R,2R,3R,5S) -3 , 5-dihydroxy-2- [ [3R) -3- hydroxy-5-phenylpentyl] cyclopentyl] -5-heptenoic acid 4- (3H-l,2-dithiole-3-thione-5-yl) -phenyl ester

(Hoc, 13E, 15S) -11, 15-dihydroxy-9-oxoprost-13-en-l-oic acid 2- (methylsulfonylthio) ethyl ester

(5Z) -7- [ (Ii?, 2R ₁ 3R ₁ 5S) -3 , 5-dihydroxy-2- [ (3R) -3- hydroxy- 5 -phenylpentyl] cyclopentyl] -5-heptenoic

acid 2- (methylsulfonylthio) ethyl ester

(llα, 13E, 155) -11, 15-dihydroxy-9-oxoprost-13 -en-l-oic acid 2- (methylsulfonylthio) ethylamide

(5Z) -7- [ (lJ?,2i?,3J?,5S) -3,5-dihydroxy-2- [3J?) -3-hydroxy- 5-phenylpentyl] cyclopentyl] -5-heptenoic acid 2- (methylsulfonylthio) ethylamide

OH

-NH-CH ₂ -CH ₂ -S-SO ₂ -CH ₃

(5Z, 9α, llα, 13S, 15S) -9, 11, 15-trihydroxy-17-phenyl- 18, 19,20-trinorprosta-5, 13-dienoic acid 2- (methylsulfonylthio) ethylamide

OH

-NH-CH ₂ -CH ₂ -S-SO ₂ -CH ₃

When the compounds include at least one asymmetric carbon atom, the products can be used in racemic mixture or in form of single enantiomer.

It is a further object of the present invention the pharmaceutical acceptable salts of compounds of formula (I) , such as for example salts with alkaline metals and alkaline earth metals, non-toxic amines and aminoacids, inorganic acids such as hydrochloric acid, phosphoric acid, etc., or organic acids such as fumaric acid, citric acid, tartaric acid, etc.

Salts of organic thiosulfonates such as, for example, S- (2-carboxyethyl) methanthiosulfonate, S- (2 -aminoethyl) methanthiosulfonate with the different prostaglandin derivatives above-described, are also part of the present invention. Salts of dithiolthiones such as, for example, 1, 3-dithiol-2- thione-5-carboxylic acid, 3-thioxo-3H-l , 2-dithiole-5- carboxylic acid, 3-thioxo-3H-l, 2-dithiole-4- carboxylic acid with the different prostaglandin derivatives above-described are also part of the

present invention.

According to the present invention it has been found that it is possible to link an organic polysulfurated group to a prostaglandin derivative for treating ocular diseases. The resulting compounds have good bioavailability, increased safety and maintain good efficacy.

The main advantages of the compounds of the present invention are related to their biological activity by topical route.

Further object of the present invention are pharmaceutical compositions comprising at least one compound of the above-said prostaglandin derivative compounds (according to the present invention as for general formula (I) and the preferred compounds as described above) including salts thereof, as an active ingredient, moreover, as a further object of the present invention, in combination with pharmaceutically acceptable adjuvant (s) or carrier (s) .

It is a further object of the present invention the use of the prostaglandin derivative compounds as for general formula (I) , and the preferred compounds as described above, as a medicament.

A further object of the present invention is the use of compounds according to the present invention, as for general formula (I) , and the preferred compounds as described above, for the preparation of a pharmaceutical composition, and therefore the corresponding method, for preventing, treating or reducing ocular diseases also in combination with other ocular agents.

The prostaglandins derivatives of the present invention can be also used, for example, for treating erectile dysfunction, cerebrovascular and cardiovascular disorders, disorders deriving from peptic ulcer and for inducing abortion.

The compounds of the present invention can be administered in the form of any pharmaceutical formulation, the nature of which will depend upon the route of administration and the nature of the disease to be treated. These pharmaceutical compositions can be prepared by conventional methods, using compatible and pharmaceutically acceptable excipients or vehicles. Examples of such compositions include capsules, tablets, syrups, powders and granulates for the preparation of extemporaneous solutions, injectable preparations, rectal, nasal, ocular,

vaginal etc .

A preferred route of administration is the ocular route.

It is a further object of the present invention the process of the synthesis of prostaglandin derivative compounds, as for general formula (I), and preferred compounds as described above, said process comprising the reaction of a prostaglandin or its derivatives with a corresponding precursor of an organic thiosulfonate or of a dithiolthione, moiety W or Y-W, or the reaction of a corresponding precursor of an organic thiosulfonate or of a dithiolthione, moiety W, with a prostaglandin or its derivative, eventually modified with Y, being said W and Y as defined above.

The method for treating glaucoma or ocular hypertension consists in contacting a compound of formula (I) with the eye in order to reduce the eye pressure. The composition contains 0.1-30 μg, and preferably 1-10 μg per application of the active substance. The prostaglandin derivative is mixed with an ophthalmologic compatible vehicle that comprises aqueous solutions, oil solutions, ointments. The vehicle may contain in addition preservatives such as

benzalkonium chloride, surfactants like polysorbate 80, liposomes, polymers such as cellulose derivatives, poly ^v inylpyrrolidone, hyaluronic acid that can be used to increase viscosity. It is also possible to use soluble or insoluble insert to administer the drug.

It is a further object of the present invention the use of prostaglandin derivative compounds of general formula (I) and the preferred compounds as described above, for preventing, treating or reducing ocular diseases, also in combination with other ocular agents, as well as the method for preventing, treating or reducing ocular diseases, said method comprising the use of prostaglandin derivative compounds of general formula (I) and the preferred compounds as described above .

The following non-limitative examples further describe the invention and enable a person ordinary skilled in the art to make and use the invention. EXAMPLE 1. Synthesis of (llα, 13E, 15S) -11, 15- dihydroxy-9-oxoprost-13-en-l-oic acid 4-(3H-l,2- dithiole-3-thione-5-yl) -phenyl ester.

Step 1: Preparation of 5- (p-hydroxyphenyl) -3H-1, 2- dithiol-3-thione .

To 280 mmol of sulphur, 40 mmol of anethole in 20 ml of dimethylacetamide are added. After heating at

145°C for 6 hours, 2.5 g of anethole dithiolethione

(ADT) are obtained. The product, washed with ether, was crystallized by ethyl acetate: melting point 110-

111 ⁰ C. Then 1.5 g of ADT are mixed with 7.5 g of pyridine HCl and the mixture is heated for 25 minutes at 215°C. After cooling, IN HCl in excess is added and the precipitate is filtered, washed and crystallized from ethanol . The obtained compound, 5- (p-hydroxyphenyl) -3H-1, 2-ditiol-3-thione, melts at 191-192°C. Step 2; 25 mg of the compound prepared in step 1 (0.11 mmol) and catalytic amount of 4-dimethylaminopyridine (DMAP) are added to a solution of (Hoc, 13E, 15S) - 11, 15-dihydroxy-9-oxoprost-13-en-l-oic acid (PGEl 0.055 mmol; 20 mg) in 1 ml of anhydrous tetrahydrofuran (THF) stirring under nitrogen at a temperature of O ⁰ C. After few minutes l-(3- dimethylaminoisopropyl) -3-ethyl-carbodiimide hydrochloride (EDAC, 0.08 mmol; 16 mg) is added and the reaction is stirred at room temperature for 15 hours. After evaporation of THF, the residue is

dissolved in chloroform and washed with water. The chloroformic solution is dried on anhydrous sodium sulphate, evaporated to dryness and the product is chromatographed on column of silica gel eluting with ethylacetate . The obtained product is red and after washing with ether, has a melting point of 101-105° C.

EXAMPLE 2. Synthesis of (5Z) -7- [ (IE, 2R, 3R, 5S) -3, 5- dihydroxy-2- [ (3R) -3-hydroxy-5-phen.ylpeii.tyl] cyclopentyl] -5-heptenoic acid 4- (3H-1, 2-dithiole-3- thione-5-yl) -phenyl ester.

39 mg of the compound prepared in Example 1 step 1 (0.17 mmol) and catalytic amount of 4- dimethylaminopyridine (DMAP) are added to a solution of (5Z) -7- [ (1R,2R,3R,5S) -3 , 5-dihydroxy-2- [ (3J?) -3- hydroxy-5-phenylpentyl] cyclopentyl] -5-heptenoic acid (latanoprost acid 0.087 mmol; 34 mg) in 1 ml of anhydrous tetrahydrofuran (THF) stirring under nitrogen at a temperature of O ⁰ C. After few minutes 1- (3-dimethylaminoisopropyl) -3-ethyl-carbodiimide hydrochloride (EDAC, 0.13 mmol; 25 mg) is added and the reaction is stirred at room temperature for 15 hours. After evaporation of THF, the residue is dissolved in chloroform and washed with water. The

chloroformic solution is dried on anhydrous sodium sulphate, evaporated to dryness and the product is chromatographed on column of silica gel with ethylacetate . After washing with ether the obtained red-coloured product, has a melting point of 91.1-92.2° C. EXAMPLE 3. Synthesis of (llα, 13E, 15S) -11, 15- dihydroxy-9-oxoprost-13-en-l-oic acid 2- (methylsulfonylthio) ethyl ester. Step 1: Synthesis of methanethiosulfonic acid S- (2- hydroxyethyl ) ester.

A solution of CH ₃ SO ₂ Cl (5.9 g) in ethanol (9.2 ml) is added dropwise to a refrigerated (-15 ⁰ C) solution of Na ₂ S (46.98 mmol) in ethanol(34.5 ml). The reaction mixture is stirred at room temperature for 12 hours. After filtration and crystallization from ethanol, sodium methanthiosulfonate, as a white solid, is obtained. The sodium methanthiosulfonate (2.5 g; 18.64 mmol) is dissolved in 30 ml of ethanol and a solution of 2-bromoethanol (2.6 ml; 37.28 mmol) in ethanol (6 ml) is added dropwise. The solution is heated at 100°C for 8 hours under nitrogen. The mixture is filtered, the solution is evaporated to dryness and the residue is dissolved in CHCl ₃ and

extracted with water.

The aqueous solution is evaporated to dryness, tetrahydrofuran (THF) is added to the residue and the obtained suspension is filtered. The THF solution is evaporated and methanethiosulfonic acid S- (2 - hydroxyethyl ) ester, as an oily yellow product, is obtained. Step 2: 22 mg of the compound prepared in step 1 (0.14 mmol) and catalytic amount of 4-dimethylaminopyridine (DMAP) are added to a solution of (llα, 13E, 15S) - 11, 15-dihydroxy-9-oxoprost-13-en-l-oic acid (PGEl 0.07 mmol; 25 mg) in 1 ml of anhydrous tetrahydrofuran (THF) stirring under nitrogen at a temperature of O ⁰ C. After few minutes 1- (3- dimethylaminoisopropyl) -3-ethyl-carbodiimide hydrochloride (EDAC, 0.10 mmol; 19.4 mg) is added and the reaction mixture is stirred at room temperature for 15 hours. After evaporation of THF, the residue is dissolved in chloroform and washed with water. The chloroformic solution is dried on anhydrous sodium sulphate, evaporated to dryness and the product is chromatographed on column of silica gel eluting with a mixture of ethylacetate/cyclohexane

(80/20) . After washing with ether the obtained red- coloured product, has a melting point of 56-58 ⁰ C. EXAMPLE 4. Synthesis of (5Z) -7- [ (112, 212, 3i2, 5S) -3, 5- dihydroxy-2- [ (312) -3-hydroxy-5-phenylpentyl] cyclopentyl] -5-heptenoic acid 2- (methylsulfonylthio) ethyl ester.

In the same manner as described in Example 3 the (5Z) -7- [ (1R,2R,3R,5S) -3 , 5-dihydroxy-2 - [ (312) -3- hydroxy-5-phenylpentyl] cyclopentyl] -5-heptenoic acid 2- (methylsulfonylthio) ethyl ester is prepared.

EXAMPLE 5. Synthesis of (llα, 13E,15S) -11, 15- dihydroxy-9-oxoprost-13-en-l-oic acid 2- (methylsulfonylthio) ethylamide. Step 1: Synthesis of S- (2-aminoethyl) methan- thiosulfonate

A solution of CH ₃ SO ₂ Cl (5.9 g) in ethanol (9.2 ml) is added dropwise to a refrigerated (-15 ⁰ C) solution of Na ₂ S (46.98 mmol) in ethanol(34.5 ml). The reaction mixture is stirred at room temperature for 12 hours. After filtration and crystallization from ethanol, sodium methanthiosulfonate, as a white solid, is obtained.

The sodium methanthiosulfonate (1.20 g; 8.9 mmol) is dissolved in 17 ml of ethanol and 2-bromoethylamine

hydrobromide (1.8 g,- 8.9 mmol) is added. The solution is heated at 100 ⁰ C for 5 hours under nitrogen. At the end of the reaction the mixture is cooled at O ⁰ C filtered to remove NaBr, and the solution is evaporated to obtain an oil that after treatment with ethanol crystallizes and gives a compound with a melting point of 112.0-112.8 ⁰ C. Step 2:

33 mg of the compound prepared in step 1 (0.14 mmol) and catalytic amount of 4-dimethylaminopyridine (DMAP) are added to a solution of (Hoc, 13E, 15S) - 11, 15-dihydroxy-9-oxoprost-13-en-l-oic acid (PGEl 0.07 mmol; 25 mg) in CH ₂ Cl ₂ stirring under nitrogen at a temperature of O ⁰ C. After few minutes l-(3- dimethylaminoisopropyl) -3 -ethyl-carbodiimide hydrochloride (EDAC, 0.1 mmol; 19.4 mg) is added and the reaction is stirred at room temperature for 24 hours. After washing with water, 0.1 N HCl, water, NaHCO ₃ in a separator funnel, the solution is dried on anhydrous sodium sulphate, filtered and evaporated to dryness _. The product is then chromatographed on column of silica gel eluting with ethylacetate/methanol (99.5:0.5). The obtained product has the following NMR: IH NMR (CDCl ₃ ): δ6.00

(m, IH) ; 5.70-5.45 (m, 2H) ; 4.10-3.95 (m, 2H) ; 3.60- 3.45 (m, 2H) ; 3.30 (s, 3H) ; 3.25 (t, 2H) ; 2.75-2.60

(m, IH); 2.40-1.10 (m, 24H); 0.9-0.70 (m, 3H). EXAMPLE 6 Synthesis of (5Z) -7- [ (IR, 2R ₁ 3R, 5S) -3, 5- dihydroxy-2- [ (3R) -3-hydroxy-5-phenylpentyl] cyclopentyl] -5-heptenoic acid 2- (methylsulfonylthio) ethylamide . 42 mg of the compound prepared in Example 5 step 1

(0.18 mmol) and catalytic amount of 4- dimethylaminopyridine (DMAP) are added to a solution of (5Z) -7- [ (1R,2R,3R,5S) -3 , 5-dihydroxy-2- [ (3R) -3- hydroxy-5-phenylpentyl] cyclopentyl] -5-heptenoic acid

(latanoprost acid) (0.09 mmol; 35 mg) in anhydrous THF, stirring under nitrogen at a temperature of O ⁰ C. After few minutes 1- (3-dimethylaminoisopropyl) -3- ethyl-carbodiimide hydrochloride (EDAC, 0.14 mmol; 26 mg) is added and the reaction is stirred at room temperature for 24 hours. After evaporation of THF, the residue is dissolved in CH ₂ Cl ₂ and the solution is washed first with water and then with 0.1 N HCl, water and finally with a sol. of NaHCO ₃ . The organic solution is dried on anhydrous sodium sulphate, filtered and evaporated to dryness, to obtain a product which is chromatographed on a column of

silica gel with ethylacetate . The obtained compound has the following ¹ H NMR (CDCl ₃ ): 87,35-7.10 (m, 5H); 6.55 (s, IH); 5.50-5.30 (m, 2H); 4.20 (s, IH); 3.96 (s, IH); 3.75-3.50 (m, 3H); 3.30 (s, 3H); 3.25 (t, 2H); 2.85-2.60 (m, 2H); 2.45-1.25 (m, 18 H). EXAMPLE 7. Synthesis of (5Z, 9α, llα, 13E, 15S) -9, 11, 15- trihydroxy-17 -phenyl-18,19,20-trinorprosta-5 , 13 - dienoic acid 2- (methylsulfonylthio) ethylamide In the same manner as described in Example 6 the (5Z, 9α, llα, 13E, 15S) -9 , 11 , 15-trihydroxy- 17-phenyl-

18, 19, 20-trinorprosta-5, 13-dienoic acid 2- (methylsulfonylthio) ethylamide is prepared. EXAMPLE 8. Biological activity Studies on rat retina The method described by Osborne N.N. et al . (2002) previously reported was used. Briefly, two groups of 16 Wistar rats (200-250 g) received either 5 μl doses of topical test compound (2% in 50% polyethylene glycol-PEG) or 5 μl of vehicle bilaterally twice a day for 2 days. On the third day N-methyl-D- aspartate (NMDA) (5 μl in sterile water) was injected intra-vitreally into a single eye of each animal. The other eye was injected with sterile water. The animals were treated then with test compound or

vehicle for 7 days. The Thy-1 antigen is associated with ganglion cells and intraocular injections of NMDA cause a loss of Thy-1 mRNA. The rats were then killed and the retinas removed for mRNA analysis for Thy-1 antigen. Results are expressed as % value to the Thy-1 mRNA levels (relative to rhodopsin) of the treated groups, taking PEG value as 100. Studies of IQP (intraocular pressure) on rabbit The method by Osborne N.N. et al. (2002) previously reported was used. Briefly, two groups of adult male New Zealand albino rabbits weighing 3-3.5 kg were used in the experiments. IOP was measured using a properly calibrated tonometer immediately after topical application of 1 drop of 0.4% benoxinate hydrochloride. The animals received a topical application of 2% of test compound or PEG and measures taken 60 minutes after. Results are expressed as % value to the IOP mmHg values of the treatment groups, taking PEG value as 100. Results that are reported in the table below (Table 1) show that the test compound markedly affects both intraocular pressure and Thy-1 mRNA loss, indicating relevant intraocular hypotensive and neuroprotective properties .

Table 1