Abstract:
Treatment of ocular hypertension by long term therapy with a prostaglandin related compound for eliminating or reducing potential iridic pigmentation.

Description:
[0001]    This application is a Continuation-In-Part of U.S. application Ser. No. 09/527,573 filed Mar. 16, 2000. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    The present invention relates to the long-term treatment and prophylactic management of intraocular pressure in human patients. More specifically, the present invention relates to the long term management of hypertension or glaucoma in the eyes of human patients, without causing pigmentation or with causing comparatively minimal pigmentation of the iris, by periodic topical ocular application of a prostaglandin related compound.  
           [0003]    Prostaglandins (hereinafter, referred to as PG(s)) are members of a class of organic carboxylic acids, which are contained in tissues or organs of human and most other animals, and exhibit a wide range of physiological activity. PGs found in nature primary PGs) generally have a prostanoic acid skeleton as shown in the formula (A):  
                         
 
           [0004]    On the other hand, some of the synthetic analogues of primary PGs have a modified skeleton. The primary PGs are classified to PGAs, PGBs, PGCs, PGDs, PGEs, PGFs, PGGs, PGHs, PGIs and PGJs according to the structure of the five-membered ring moiety, and further classified into the following three types by the number and position of the unsaturated bond at the carbon chain moiety:  
           [0005]    Subscript 1: 13,14-unsaturated-15-OH  
           [0006]    Subscript 2: 5,6- and 13,14-diunsaturated-15-OH  
           [0007]    Subscript 3: 5,6-, 13,14-, and 17,18-triunsaturated-15-OH.  
           [0008]    Further, the PGFs are classified, according to the configuration of the hydroxyl group at the 9-position, into α type (the hydroxyl group is of an α-configuration) and β type (the hydroxyl group is of β-configuration).  
           [0009]    In addition, some 15-keto (i.e. having an oxo group at position 15 in place of the hydroxy group) prostaglandins and 13,14-dihydro-15-keto-prostaglandins are known as substances naturally produced by enzymatic reactions during in vivo metabolism of primary PGs. 15-keto PGs have been disclosed in, for example, EP-A-0281239, EP-A-0281480, EP-A-0289349, EP-A-0453127 and EP-A-0690049. These cited references are herein incorporated by reference.  
           [0010]    At present, Latanoprost is available commercially in the United States for use as a topical ocular hypotensive agent. Chemically, Latanoprost is a 13,14-dihydro-17-phenyl-18,19,20-trinor PGF 2α  isopropyl ester. One side effect of Latanoprost is a brown pigmentation of the iris found in about 10% or more of the human patients treated with Latanoprost for about three or more months for management of elevated intraocular pressure. Latanoprost possesses as substantial specific binding affinity for the FP receptor. Selen et al have reported that PGF 2 α -IE, PGE 2 -IE and latanoprost induced increased iridial pigmentation in cynomolgus monkeys (Survey of Ophthalmology, 41, supplement 2, S125-S128 (1997)). (“IE” means isopropyl ester.) Unoprostone isopropyl ophthalmic solution (Rescula®) has been commercially available outside Europe and the United States for topical application in the treatment of ocular hypertension. Unoprostone isopropyl is a docosanoid, namely 13,14-dihydro-15-keto-20-ethyl PGF 2α  isopropyl ester. To the inventor&#39;s best knowledge, Resucla® has not been commercially used by Caucasians in the management of ocular hypertension or glaucoma by its periodic topical application to the eye at least once a day for a period of at least six months, more than one year prior to the filing date of this application. Preliminary results regarding no iridic pigmentation from a long term monkey trial with Unoprostone isopropyl have been published. Resucla® exhibits substantial absence of FP receptor stimulatory activity.  
           [0011]    15-keto-latanoprost (13,14-dihydro-15-keto-17-phenyl-18, 19, 20-trinor PGF 2α  isopropyl ester) is a promising candidate for use as a topical ocular hypotensive drug. Short term studies of its use have been reported in U.S. Pat. No. 5,321,128.  
         SUMMARY OF THE INVENTION  
         [0012]    The present invention provides methods for the long-term treatment and prophylactic management of ocular hypertension and glaucoma in human patients without causing pigmentation or with causing less pigmentation than latanoprost of the patient&#39;s iris, by periodic topical administration of a prostaglandin related compound.  
           [0013]    According to the present invention, the term “prostaglandin related compound” (hereinafter, referred as “PG related compound”) includes any of derivatives or analogs (including substituted derivatives) of a compound having the prostanoic acid basic structure irrespective of the configuration of the 5-membered ring, number of double bonds in the α or ω-chain, presence or absence of hydroxy and oxo groups or any other substituent, or any other modification.  
           [0014]    The nomenclature of the PG related compounds used herein is based on the numbering system of the prostanoic acid skeleton represented in the above formula (A).  
           [0015]    The formula (A) shows a basic skeleton of 20 carbon atoms, but the PG related compounds in the present invention are not limited to those having a 20 carbon atom skeleton. In the formula (A), the numbering of the carbon atoms which constitute the basic skeleton of the PG compounds starts at the carboxylic acid (numbered 1), and carbon atoms in the α-chain are numbered 2 to 7 towards the five-membered ring, those in the ring are 8 to 12, and those in the ω-chain are 13 to 20. When the number of carbon atoms is decreased in the α-chain, the number is deleted in the order starting from position 2; and when the number of carbon atoms is increased in the α-chain, compounds are named as substitution compounds having respective substituents at position 2 in place of carboxy group (C-1). Similarly, when the number of carbon atoms is decreased in the ω-chain, the number is deleted in the order starting from position 20; and when the number of carbon atoms is increased in the ω-chain, the carbon atoms beyond position 20 are named as substituents. Stereochemistry of the compounds is the same as that of the above formula (A) unless otherwise specified.  
           [0016]    In general, each of the terms PGD, PGE and PGF represents PG compounds having hydroxy group(s) at positions 9 and/or 11, but in the present specification, these terms also include those PG related compounds having substituents other than the hydroxy group at positions 9 and/or 11. Such compounds are referred to as 9-dehydroxy-9-substituted-PG compounds or 11-dehydroxy-11-substituted-PG compounds. A PG compound having hydrogen in place of the hydroxy group is simply named as 9- or 11-dehydroxy compound.  
           [0017]    As stated above, the nomenclature of the PG related compounds is based on the prostanoic acid skeleton. However, in case the compound has a similar partial construction as a prostaglandin, the abbreviation of “PG” may be used. Thus, a PG compound of which α-chain is extended by two carbon atoms; that is, having 9 carbon atoms in the α-chain, is named as 2-decarboxy-2- (2-carboxyethyl)-PG compound. Similarly, a PG compound having 11 carbon atoms in the α-chain is named as 2-decarboxy-2- (4-carboxybutyl)-PG compound, and a PG compound having 10 carbon atoms in the ω-chain is named as 20-ethyl-PG compound. These compounds, however, may also be named according to the IUPAC nomenclatures.  
           [0018]    The PG related compounds used in the present invention may include any of PG derivatives or analogs. Accordingly, for example, a PG 1  compound having a double bond at 13-14 position and a hydroxy group at 15-position, a PG 2  compound having another double bond at 5-6 position, a PG 3  compound having further double bond at 17-18 position, a 15-keto-PG compound having an oxo group in place of the hydroxy group at the 15-position, a 15-dehydroxy-PG compound having a hydrogen atom in place of the hydroxy group at the 15-position, or the corresponding 13,14-dihydro-PG compounds wherein in each type of compound the double bond at 13-14 position is single bond, or the corresponding 13,14-didehydro-PG compounds wherein in each type of compound the double bond at the 13-14 position is a triple bond. Moreover, examples of substituted compounds and derivatives include a compound wherein the terminal carboxyl group in the α-chain of the above described compound is esterified, a physiologically acceptable salt thereof, a compound wherein the number of carbon atoms in the α- or ω-chain is decreased or increased, a compound having side chains (e.g., 1 to 3 carbon atoms) on α- or ω-chains, a compound having substituent(s) such as hydroxy, halogen, lower alkyl, hydroxy(lower)alkyl, and oxo, or double bond(s) on the five-membered ring, a compound having substituent(s), such as halogen, oxo, aryl and heterocyclic on the α-chain, a compound having substituents such as halogen, oxo, hydroxy, lower alkoxy, lower alkanoyloxy, cyclo(lower)alkyl, cyclo(lower)alkyloxy, aryl, aryloxy, heterocyclic group and heterocyclic-oxy group on the ω-chain, and a compound having substituent such as lower alkoxy, lower alkanoyloxy, cyclo(lower)alkyl, cyclo(lower)alkyloxy, aryl, aryloxy, heterocyclic group and heterocyclic-oxy group at the terminal of the ω-chain of which is shorter, the same as or longer than that of normal prostanoic acid.  
           [0019]    In preferred embodiments, the human patients are of the Caucasian race.  
           [0020]    In preferred embodiments, the periodic administration is at least once a day for at least six months.  
           [0021]    In another preferred embodiment of the invention, the compound administered is a docosanoid.  
           [0022]    In yet another preferred embodiment of the invention, the compound administered is Unoprostone isopropyl.  
           [0023]    In still another preferred embodiment of the invention, the compound administered is 15-keto-latanoprost.  
         DETAILED DESCRIPTION OF THE INVENTION  
         [0024]    The present invention is directed to the long-term care and management of intraocular pressure and glaucoma in human patients. Latanoprost, 13,14-dihydro-17-phenyl-18,19, 20-trinor PGF 2α  isopropyl ester, has been used in such treatment, but causes brown pigmentation of the iris of Caucasians in a significant number of patients (10% or more). Since it is not believed at present possible to predict with relative certainty in which patient iridic pigmentation will occur, this is a significant side effect in a color-conscious world, especially for female patients. The iridic pigmentation usually occurs by three or more months with continuous treatment, i.e., periodic administration on a daily basis. It is believed that the iridic pigmentation results from latanoprost&#39;s high specific binding affinity for the prostaglandin FP or EP receptor. ( Journal of Japan Glaucoma Society,  5, 136 (1995)  
           [0025]    Now, it has been found that a prostaglandin related compound of the present invention which substantially does not stimulate the prostaglandin FP receptor or possesses an FP specific affinity one-tenth or less than that of latanoprost and is otherwise usable as a topically administered ocular hypotensive, can be safely administered to humans over prolonged time periods without causing dark colored iridic pigmentation. Certain of these compounds are those in which carbon atom number 15 is substituted by an oxo group (15-keto compounds), or those in which carbon atom number 15 is substituted by a hydroxy group and the omega chain beyond carbon atom number 15 contains a straight chain of at least 6 carbon atoms or a straight chain of at least 3 carbon atoms with a ring at the terminal of the omega chain. As above discussed, the compounds of this invention can safely be administered topically for ocular hypotensive effect to human patients over prolonged time periods without causing the brown iridic pigmentation found with Latanoprost.  
           [0026]    Prostaglandin related compounds of the present invention and of the following formula (I) are one preferred embodiment.  
                         
 
           [0027]    wherein W 1 , W 2  and W 3  are carbon or oxygen atoms,  
           [0028]    L, M and N are hydrogen atom, hydroxy, halogen atom, lower alkyl, lower alkoxy, hydroxy(lower)alkyl, or oxo, wherein at least one of L and M is a group other than hydrogen, and the five-membered ring may have at least one double bond;  
           [0029]    A is —CH 2 OH, —COCH 2 OH, —COOH or a functional derivative thereof;  
           [0030]    B is single bond, —CH 2 —, —CH 2 —CH 2 —, —CH═CH—, —C≡C—, —CH 2 —CH 2 —CH 2 —, —CH═CH—CH 2 —, —CH 2 —CH═CH—, —C≡C—CH 2 —, or —CH 2 —C≡C—;  
           [0031]    R 1  is a saturated or unsaturated bivalent lower or medium aliphatic hydrocarbon residue, which is unsubstituted or substituted with halogen, an alkyl group, hydroxy, oxo, aryl or heterocyclic group ; and  
           [0032]    Ra is a saturated or unsaturated lower or medium aliphatic hydrocarbon residue, which is unsubstituted or substituted with halogen atom, oxo, hydroxy, lower alkyl, lower alkoxy, lower alkanoyloxy, cyclo(lower)alkyl, cyclo(lower)alkyloxy, aryl, aryloxy, heterocyclic group or hetrocyclic-oxy group; cyclo(lower)alkyl; cyclo(lower)alkyloxy; aryl; aryloxy; heterocyclic group; heterocyclic-oxy group.  
           [0033]    A group of particularly preferable compounds among the above described compounds is represented by the general formula (II):  
                         
 
           [0034]    wherein L, M, R 1 , A and B are the same definitions described above.  
           [0035]    X 1  and X 2  are hydrogen, lower alkyl, or halogen;  
           [0036]    R 2  is a single bond or lower alkylene; and  
           [0037]    R 3  is lower alkyl, lower alkoxy, cyclo(lower)alkyl, cyclo(lower)alkyloxy, aryl, aryloxy, heterocyclic group or heterocyclic-oxy group.  
           [0038]    Another preferred embodiment of this invention resides in prostaglandin related compounds of the present invention and of the formula (III):  
                         
 
           [0039]    wherein W 1 , W 2  and W 3  are carbon or oxygen atoms,  
           [0040]    L, M and N are hydrogen atom, hydroxy, halogen atom, lower alkyl, lower alkoxy, hydroxy(lower)alkyl, or oxo, wherein at least one of L and M is a group other than hydrogen, and the five-membered ring may have at least one double bond;  
           [0041]    A is —CH 2 OH, —COCH 2 OH, —COOH or a functional derivative thereof;  
           [0042]    B is single bond, —CH 2 —, —CH 2 —CH 2 —, —CH═CH—, —C≡C—, —CH 2 —CH 2 —CH 2 —, —CH═CH—CH 2 —, —CH 2 —CH═CH—, —C≡C—CH 2 —, or —CH 2 —C≡C—;  
           [0043]    R 1  is a saturated or unsaturated bivalent lower or medium aliphatic hydrocarbon residue, which is unsubstituted or substituted with halogen, an alkyl group, hydroxy, oxo, aryl or heterocyclic group;  
           [0044]    Z is  
                         
 
           [0045]    wherein R 4  and R 5  are hydrogen atom, hydroxy, halogen atom, lower alkyl, lower alkoxy or hydroxy(lower)alkyl, wherein R 4  and R 5  are not hydroxy, lower alkoxy and/or hydroxy (lower) alkyl at the same time; and  
           [0046]    Ra′ is a saturated or unsaturated C5-C10 aliphatic hydrocarbon residue, which is unsubstituted or substituted with halogen atom, oxo, hydroxy, lower alkyl, lower alkoxy, lower alkanoyloxy, cyclo(lower)alkyl, cyclo(lower)alkyloxy, aryl, aryloxy, heterocyclic group or hetrocyclic-oxy group; cyclo(lower)alkyl; cyclo(lower)alkyloxy; aryl; aryloxy; heterocyclic group; or heterocyclic-oxy group.  
           [0047]    The compounds used with the present invention can be of the prostaglandins A, B, C, D, E, F, or J type and include subtypes 1, 2, and 3, all as explained in U.S. Pat. No. 5,001,153, the entire content of which is incorporated herein by reference. Compounds usable in the present invention are described in U.S. Pat. No. 5,001,153, and in U.S. Pat. No. 5,312,128, including their ophthalmic preparations.  
           [0048]    In the above formula, the term “unsaturated” in the definitions for R 1 , Ra and Ra′ is intended to include at least one or more double bonds and/or triple bonds that are isolatedly, separately or serially present between carbon atoms of the main and/or side chains. According to the usual nomenclature, an unsaturated bond between two serial positions is represented by denoting the lower number of the two positions, and an unsaturated bond between two distal positions is represented by denoting both of the positions.  
           [0049]    The term “lower or medium aliphatic hydrocarbon” refers to a straight or branched chain hydrocarbon group having 1 to 14 carbon atoms (for a side chain, 1 to 3 carbon atoms are preferable) and preferably 1 to 10, especially 1 to 8 carbon atoms for R 1  and 1 to 10, especially 1 to 8 carbon atoms for R a .  
           [0050]    The term “halogen atom” covers fluorine, chlorine, bromine and iodine. Particularly preferable is a fluorine atom.  
           [0051]    The term “lower” throughout the specification is intended to include a group having 1 to 6 carbon atoms unless otherwise specified.  
           [0052]    The term “lower alkyl” refers to a straight or branched chain saturated hydrocarbon group containing 1 to 6 carbon atoms and includes, for example, methyl, ethyl, propyl, isopropyl, butyl, isobutyl, t-butyl, pentyl and hexyl.  
           [0053]    The term “lower alkoxy” refers to a group of lower alkyl-O-, wherein lower alkyl is as defined above.  
           [0054]    The term “hydroxy(lower)alkyl” refers to a lower alkyl as defined above which is substituted with at least one hydroxy group such as hydroxymethyl, 1-hydroxyethyl, 2-hydroxyethyl and 1-methyl-1-hydroxyethyl.  
           [0055]    The term “lower alkanoyloxy” refers to a group represented by the formula RCO—O—, wherein RCO— is an acyl group formed by oxidation of a lower alkyl group as defined above, such as acetyl.  
           [0056]    The term “cyclo(lower)alkyl” refers to a cyclic group formed by cyclization of a lower alkyl group as defined above but contains three or more carbon atoms, and includes, for example, cyclopropyl, cyclobutyl, cyclopentyl and cyclohexyl.  
           [0057]    The term “cyclo(lower)alkyloxy” refers to the group of cyclo(lower)alkyl-O-, wherein cyclo(lower)alkyl is as defined above.  
           [0058]    The term “aryl” may include unsubstituted or substituted aromatic hydrocarbon rings (preferably monocyclic groups), for example, phenyl, naphthyl, tolyl, xylyl. Examples of the substituents are halogen atom, lower alkoxy and halo(lower)alkyl, wherein halogen atom and lower alkyl are as defined above.  
           [0059]    The term “aryloxy” refers to a group represented by the formula ArO—, wherein Ar is aryl as defined above.  
           [0060]    The term “heterocyclic group” may include mono- to tri-cyclic, preferably monocyclic heterocyclic group which has a 5 to 14, preferably 5 to 10 membered ring having optionally substituted carbon atom(s) and 1 to 4, preferably 1 to 3, of 1 or 2 types of hetero atoms selected from nitrogen atom, oxygen atom and sulfer atom. Examples of the heterocyclic group include furyl, thienyl, pyrrolyl, oxazolyl, isoxazolyl, thiazolyl, isothiazolyl, imidazolyl, pyrazolyl, furazanyl, pyranyl, pyridyl, pyridazyl, pyrimidyl, pyrazyl, 2-pyrrolinyl, pyrrolidinyl, 2-imidazolinyl, imidazolidinyl, 2-pyrazolinyl, pyrazolidinyl, piperidino, piperazinyl, morpholino, indolyl, benzothienyl, quinolyl, isoquinolyl, puryl, quinazolinyl, carbazolyl, acridinyl, phenanthridinyl, benzimidazolyl, benzimidazolonyl, benzothiazolyl, phenothiazinyl. Examples of the substituent in this case include halogen, and halogen substituted lower alkyl group, wherein halogen atom and lower alkyl group are as described above.  
           [0061]    The term “heterocyclic-oxy group” means a group represented by the formula HcO—, wherein Hc is a heterocyclic group as described above.  
           [0062]    The term “functional derivative” of A includes salts (preferably pharmaceutically acceptable salts), ethers, esters and amides.  
           [0063]    Suitable “pharmaceutically acceptable salts” include conventionally used non-toxic salts, for example a salt with an inorganic base such as an alkali metal salt (such as sodium salt and potassium salt), an alkaline earth metal salt (such as calcium salt and magnesium salt), an ammonium salt; or a salt with an organic base, for example, an amine salt (such as methylamine salt, dimethylamine salt, cyclohexylamine salt, benzylamine salt, piperidine salt, ethylenediamine salt, ethanolamine salt, diethanolamine salt, triethanolamine salt, tris(hydroxymethylamino)ethane salt, monomethyl-monoethanolamine salt, procaine salt and caffeine salt), a basic amino acid salt (such as arginine salt and lysine salt), tetraalkyl ammonium salt and the like. These salts may be prepared by a conventional process, for example from the corresponding acid and base or by salt interchange.  
           [0064]    Examples of the ethers include alkyl ethers, for example, lower alkyl ethers such as methyl ether, ethyl ether, propyl ether, isopropyl ether, butyl ether, isobutyl ether, t-butyl ether, pentyl ether and 1-cyclopropyl ethyl ether; and medium or higher alkyl ethers such as octyl ether, diethylhexyl ether, lauryl ether and cetyl ether; unsaturated ethers such as oleyl ether and linolenyl ether; lower alkenyl ethers such as vinyl ether, allyl ether; lower alkynyl ethers such as ethynyl ether and propynyl ether; hydroxy(lower)alkyl ethers such as hydroxyethyl ether and hydroxyisopropyl ether; lower alkoxy (lower)alkyl ethers such as methoxymethyl ether and 1-methoxyethyl ether; optionally substituted aryl ethers such as phenyl ether, tosyl ether, t-butylphenyl ether, salicyl ether, 3,4-di-methoxyphenyl ether and benzamidophenyl ether; and aryl(lower)alkyl ethers such as benzyl ether, trityl ether and benzhydryl ether.  
           [0065]    Examples of the esters include aliphatic esters, for example, lower alkyl esters such as methyl ester, ethyl ester, propyl ester, isopropyl ester, butyl ester, isobutyl ester, t-butyl ester, pentyl ester and 1-cyclopropylethyl ester; lower alkenyl esters such as vinyl ester and allyl ester; lower alkynyl esters such as ethynyl ester and propynyl ester; hydroxy(lower)alkyl ester such as hydroxyethyl ester; lower alkoxy (lower) alkyl esters such as methoxymethyl ester and 1-methoxyethyl ester; and optionally substituted aryl esters such as, for example, phenyl ester, tosyl ester, t-butylphenyl ester, salicyl ester, 3,4-di-methoxyphenyl ester and benzamidophenyl ester; and aryl(lower)alkyl ester such as benzyl ester, trityl ester and benzhydryl ester. Examples of the amides are mono- or di-lower alkyl amides such as methylamide, ethylamide and dimethylamide; arylamides such as anilide and toluidide; and alkyl- or aryl-sulfonylamides such as methylsulfonylamide, ethylsulfonyl-amide and tolylsulfonylamide.  
           [0066]    Preferred examples of L and M include hydroxy and oxo, and especially, M and L are hydroxy to provide a 5-membered ring structure of, so called, PGF type.  
           [0067]    Preferred A is —COOH, —CH 2 OH, or its pharmaceutically acceptable salt, ester, ether or amide thereof.  
           [0068]    Preferred example of X 1  and X 2  is that at least one of them is halogen, more preferably, both of them are halogen, especially fluorine, that provides a structure of, so called 16,16-difluoro type.  
           [0069]    Preferred R 1  is an unsubstituted saturated or unsaturated bivalent lower-medium aliphatic hydrocarbon residue. It may preferably have 1-10 carbon atoms, more preferably, 2-8 carbon atoms.  
           [0070]    Examples of R 1  include, for example, the following groups:  
           [0071]    —CH 2 —CH 2 —,  
           [0072]    —CH 2 —CH 2 —CH 2 —CH 2 —,  
           [0073]    —CH 2 —CH═CH—CH 2 —,  
           [0074]    —CH 2 —C≡C—CH 2 —,  
           [0075]    —CH 2 —CH 2 —CH 2 —CH 2 —CH 2 —,  
           [0076]    —CH 2 —CH═CH—CH 2 —CH 2 —,  
           [0077]    —CH 2 —C≡C—CH 2 —CH—,  
           [0078]    —CH 2 —CH 2 —CH 2 —CH 2 —CH 2 —CH 2 —,  
           [0079]    —CH 2 —CH═CH—CH 2 —CH 2 —CH 2 —,  
           [0080]    —CH 2 —CH 2 —CH 2 —CH 2 —CH═CH—,  
           [0081]    —CH 2 —C≡C—CH 2 —CH 2 —CH 2 —,  
           [0082]    —CH 2 —CH 2 —CH 2 —CH 2 —CH(CH 3 )—CH 2 — 
           [0083]    —CH 2 —CH 2 —CH 2 —CH 2 —CH 2 —CH 2 —CH 2 —CH 2 —,  
           [0084]    —CH 2 —CH═CH—CH 2 —CH 2 —CH 2 —CH 2 —CH 2 —,  
           [0085]    —CH 2 —CH 2 —CH 2 —CH 2 —CH 2 —CH 2 —CH═CH—,  
           [0086]    —CH 2 —C≡C—CH 2 —CH 2 —CH 2 —CH 2 —CH 2 —,  
           [0087]    —CH 2 —CH 2 —CH 2 —CH 2 —CH 2 —CH 2 —CH 2 (CH 3 )—CH 2 — 
           [0088]    Preferred R 2  is a single bond or a saturated or unsaturated bivalent lower to medium aliphatic hydrocarbon residue, which may preferably have 1-10 carbon atoms, more preferably 1-8 carbon atoms, especially 1-6 alkylene.  
           [0089]    Preferred R 3  is a hydrogen atom, aryl or aryloxy.  
           [0090]    Preferred Ra is a hydrocarbon containing 1-10 carbon atoms, more preferably, 1-8 carbon atoms and, especially, that having 7 carbon atoms beyond carbon atom number 15.  
           [0091]    Preferred Ra′ is a straight chain beyond carbon atom number 15 of at least 6 carbon atoms, or at least 3 carbon atoms with a ring, more preferably a phenyl ring, at the terminal of the omega chain.  
           [0092]    The configuration of the ring and the α- and/or ω chains in the present invention may be the same as or different from that of the primary PGs. However, the present invention also includes a mixture of a compound having a primary type configuration and a compound of a non-primary type configuration.  
           [0093]    When a 15-keto-PG compound of the present invention has for example a single bond between carbon atom number 13 and 14, the compound may be in the keto-hemiacetal equilibrium by formation of a hemiacetal between hydroxy at position 11 and oxo at position 15.  
           [0094]    If such tautomeric isomers as above are present, the proportion of both tautomeric isomers varies with the structure of the rest of the molecule or the kind of the substituent present. Sometimes one isomer may predominantly be present in comparison with the other. However, it is to be appreciated that the compounds used in the invention include both isomers. Further, while the compounds used in the invention may be represented by a structure formula or name based on keto-type regardless of the presence or absence of the isomers, it is to be noted that such structure or name does not intend to exclude the hemiacetal type compound.  
           [0095]    The present invention includes any of the isomers such as the individual tautomeric isomers, a mixture thereof, or the optical isomers, a mixture thereof, a racemic mixture, and other steric isomers useful for the same purpose.  
           [0096]    In the method of the present invention, the above-described compounds are topically administered to the affected eye once or twice a day for at least six months, up to a time period as long as required, to complete treatment for elevated ocular pressure or glaucoma, as needed, or to maintain a prophylactic level for six months or longer, without causing iridic pigmentation, especially the brown pigmentation caused by long term use of Latanoprost.  
           [0097]    The ophthalmic preparation of the present invention will usually have a concentration of less than approximately 0.20% (w/v) of active compound. Preferred concentrations are usually within the concentration range of about 0.00005 to 0.18% (w/v). 
       
    
    
     EXAMPLE 1  
       [0098]    813 human subjects, mostly Caucasian, were studied for about one year. One drop of 0.15% Rescula® was administered to each treated eye twice a day. After about the first six months of the trial, there was no reported increase in brown pigmentation of the iris.  
       EXAMPLE 2  
     In Vitro Functional Receptor Studies  
       [0099]    FP-receptor Activity  
         [0100]    Functional FP-receptor studies were performed using iris sphincter muscles from cat eyes. The eyes were either used directly after enucleation or stored in ice cold saline overnight. The iris sphincter muscles were prepared, cut in halfs, and mounted in thermostated (37° C.) tissue baths with oxygenated modified Kreb&#39;s solution containing indomethacin (2.8×10 −6  M), atropine (10 −7  M) and propranolol (10 −7  M). A resting tension of 150 mg was applied, and the contractile force was measured isometrically after cumulative dosing of test compounds. A manual or automated tissue bath system (Buxco, STC 400) was used for the experiments. For each tissue sample the maximal response was normalized to 100%. The mean response of two to four different preparations was calculated.  
         [0101]    EP 1 -receptor Activity  
         [0102]    Iris sphincter muscles from bovine eyes were used for studies of EP 1 -receptor responses. Freshly enucleated bovine eyes were transported on ice from a slaughterhouse. The experiments were performed essentially in the same way as with cat iris sphincters, but since bovine iris sphincter expresses both EP 1  and TP-receptors, a TP-receptor agonist (GR32 191B) was added to the tissue baths in concentration of 0.1 μ.M.  
         [0103]    EP2-receptor activity  
         [0104]    Segments of guinea-pig ileum were used to study the effect on EP 2 -receptors. Male guinea pigs were killed with a blow to the head and bled from the carotid arteries. Circular rings (2-3 mm wide) were taken from the ileum about 10 cm from the caecum, A resting tension of 1 g was applied and the preparation was stimulated by using a Gras S88 stimulator delivering trains of square pulses (frequency 7.5 Hz, pulse duration 0.1 msec, train duration 4 sec) to two parallel platinum electrodes in the bath. The voltage over the electrodes was approximately 20 V, and the interval between trains was 100 seconds. The peak contractile force at each stimulation train was measured. Test compounds were added cumulatively, and the inhibitory effect on the muscle twitch was evaluated. A response was taken when three successive peaks had a similar height.  
         [0105]    EP 3 -receptor Activity  
         [0106]    Guinea-pig vas deferens was used to assess the effect on EP 3 -receptors. Tissue segments of about 10 mm were mounted in tissue baths and the experiments were performed essentially in the same way as described for the guinea-pig circular ileum.  
         [0107]    Platelet Studies of TP and IP/DP Receptor Activity  
         [0108]    The activity of test compounds on platelet aggregation was performed on samples from guinea-pig blood. Blood was collected in Venoject tubes containing sodium citrate (to give a concentration of 10 mM) and centrifuged at 200 G for 10 minutes to obtain platelet rich plasma (PRP). The PRP was removed and the remainder was further centrifuged 2000 G for 15 minutes and the supernatant was used as platelet poor plasma (PPP). Platelet aggregation was measured in a Chrono-Log aggregometer using PPP as a blank. 500 μl PRP was incubated for 2 minutes at 37° C. and 5 μl of the test solution was added. The maximal change in light transmission was recorded.  
         [0109]    Aggregation of guinea-pig thrombocytes was used to measure the effect on TP receptors. The maximal change in light transmission for each test solution was calculated in percent of the maximal aggregation obtained with stable TxA2 analogue U46619 (3 μM) in the same batch of PRP.  
         [0110]    The activity on IP and DP-receptors was determined from the ability of the compounds to inhibit ADP induced aggregation of guinea pig PRP. The test substance (5 μl) was added to 500 μl PRP and incubated at 37° C. for two minutes. ADP (final concentration 10 μM) was added and the maximal change in light transmission induced by ADP in absence and presence of the test drug in the same batch of PRP was measured and expressed in percent.  
         [0111]    Concentration-effect curves were fitted to the data using the logistic sigmoid function.  
       Table 2  
     Prostaglandin Receptor Profile of Latanoprost Acid and 15-keto-latanoprost Acid Based on EC 50  Values (moles/l) Obtained in Smooth Muscle Bath Experiments  
       [0112]    [0112]                                               PG-analogues   FP   EP1   EP2   EP3                   Latanoprost   1.0 × 10 −8     4.9 × 10 −6     5.3 × 10 −4     2.8 × 10 −5         Acid       15-keto   2.6 × 10 −7     2.8 × 10 −5     &gt;10 −4     &gt;10 −4         Latanoprost       Acid                    
         [0113]    The results in Table 2 indicate that a concentration of latanoprost acid of only 1.0×10 −8 M is needed to stimulate the FP-receptor at 50% efficacy compared to significantly higher concentrations for the other prostaglandin receptors. This means that latanoprost is a selective agonist for the FP receptor and exerts its biological effect primarily through stimulation of this receptor when administered to the eye in clinical doses. A considerably higher concentration of 2.6×10 −7  M was required for 15-keto-Iatanoprost acid for a similar stimulation of the FP-receptor. Accordingly, the receptor profile study of Table 2 provides evidence that 15-keto-latanoprost acid is at least ten times less potent than latanoprost acid with respect to the activity on thc FP receptor, and has virtually no activity on the other prostaglandin receptors (EP 1  EP 2 , and EP 3 .).  
       EXAMPLE 3  
     Affinity Profile of Unoprostone for Prostaglandin Receptors  
       [0114]    The studies undertaken were to determine whether unoprostone isopropyl or its metabolite (the acid obtained by hydrolysis of the isopropyl ester) has affinity for any prostaglandin receptor.  
         [0115]    Ligand Binding Assays and Signal Transduction Studies  
         [0116]    In ligand binding studies, the specificity of labeled unoprostone isopropyl and the metabolite binding to prostaglandin receptor sites in bovine corpus luteal membranes was determined. This tissue expresses most of the PG receptors including an abundance of FP receptors. In signal transduction studies, the mobilization of intracellular calcium using Fluorescence Imaging technique in the primary culture of human ciliary muscle cells and cyclic AMP generation in rabbit iris-ciliary body was measured.  
       METHODS  
       [0117]    1) Ligand Binding Assay Method  
         [0118]    This method is well described in the literature. Briefly, 8-16 nM  3 H-PGF 2 α or  3 H-unoprostone isopropyl or the metabolite was incubated in the presence or absence of 1,000 fold excess of unlabeled PGF 2 α or unoprostone isopropyl or its metabolite with bovine corpus luteal membranes. Free unbound ligands were separated by rapid filtration using a millipore filtration assembly. Membrane bound radioactivity retained by the filter was counted. It is important to define the following terms for appreciation of the binding data:  
         [0119]    Total binding is defined as the amount bound in the absence of unlabeled ligand.  
         [0120]    Specific binding is defined as the binding displaced by unlabeled ligand.  
         [0121]    Non-specific binding is the binding not displaced by unlabeled ligand.  
         [0122]    2) Signal Transduction Methods Intracellular Calcium Mobilization  
         [0123]    Human ciliary muscle cells at confluency were loaded with Fura 2-AM. Cells in a petri dish were put in a jacketed chamber mounted on the microscope platform. The chamber was maintained at 37° C. by thermostatically controlled water circulating through the chamber jacket. The cells were then exposed to the excitation wavelengths of 334 and 380 nm with an emission wavelength of 510 nm. Cells were perfused with HEPES buffer with or without test compounds. The intracellular calcium was visualized and photographed using Attofluor RatioVision software program and Zeiss fluorescence microscope.  
       RESULTS  
       [0124]    1) Binding Studies  
         [0125]    To optimize the specific binding of  3 H-unoprostone isopropyl or the metabolite, initially binding was determined as the function of time, membrane and radioligand concentrations in the presence or absence of unlabeled unoprostone or PGF 2α . At 5 minutes, total binding was 21.0 fmoles/mg protein, which did not increase with time up to 60 minutes in bovine corpus luteal membranes.  
         [0126]    Tables I and II showed that total binding of  3 H-unoprostone isopropyl increased with concentrations of the membrane and radioligand but none of the binding was displaced by unlabeled unoprostone isopropyl or PGF 2α  suggesting no specific binding.  
         [0127]    Table I. Total Binding of  3 H-unoprostone isopropyl in bovine corpus luteal membranes as a function of membrane concentration.  
                                                   Protein Conc   Total binding: fmoles/mg protein                            50 μg   13.0 ± 2.0 (3)           100 μg   23.0 ± 6.0 (3)           200 μg   32.0 ± 8.0 (3)                      
 
         [0128]    Unlabeled unoprostone isopropyl or PGF 2 , did not displace any of the above binding.  
       Table II  
     Binding of  3 H-unoprostone Isopropyl and  3 H-PGF 2α  in Bovine Corpus Luteal Membranes as a Function of Concentration  
       [0129]    [0129]                                                                                 3 H-unoprostone isopropyl                    Specific     3 H-PGF2α                Total Binding   Binding       Total Binding   Specific Binding       Conc   ƒmoles/mg   fmoles/mg   Conc   fmoles/mg   fmoles/mg       (nM)   protein   protein   (mM)   protein   protein                8.0   19.4 ± 2.0 (3)   0   2.0   150.0 ± 16.0 (3)   120.0 ± 15.0 (3)       16.0   25.5 ± 4.0 (3)   0   4.0   325.0 ± 25.0 (3)   261.0 ± 27.0 (3)       32.0   40.0 ± 7.0 (3)   0   8.0   505.0 ± 75.0 (3)   423.0 ± 40.0 (3)                    
         [0130]    There were no specific binding sites for unoprostone isopropyl as shown in the Table III because none of the unlabeled unoprostone isopropyl concentrations displaced the bound  3 H-unoprostone isopropyl. In contrast,  3 H-PGF 2 , was bound specifically to its binding sites. Competition studies showed that 17-Phenyl trinor PGE 1  (EP 1 ), Butaprost (EP 2 ), sulprostone (EP 3 ), iloprost (IP), U46619 (TP) and BW245C (DP) did not displace  3 H-unoprostone isopropyl from the binding sites suggesting that unoprostone isopropyl does not bind to DP, EP 1 , EP 2 , EP 3 , IP and TP receptor sites. The metabolite has similar binding profiles as unoprostone isopropyl, i.e. it does not bind to any PG receptor sites.  
       Table III  
     Competition for  3 H-unoprostone Isopropyl or PGF 2 a Binding Sites by Prostaglandin Receptor Agonists  
       [0131]    [0131]                                                       Total  3 H-                       Competing   unoprostone   Specific       Ligand   isopropyl   Binding of   Competing   Total  3 H-PGF 2 α       Unoprostone   binding     3 H-   Ligand   binding   Specific Binding       Isopropyl   ƒmoles/mg   unoprostone   PGF 2 α   nmoles/mg   fmoles/mg       (μM)   protein   isopropyl   (μM)   Protein   Protein                   2.5   7.0   0   0.062   0.56   0.07       5.0   6.5   0   0.25   0.56   0.15       8.0   6.7   0   0.5   0.56   0.25       16.0    7.6   0   8.0   0.56   0.42                    
         [0132]    2) Second Messenger Study: Calcium Mobilization  
         [0133]    Unoprostone isopropyl or the metabolite at concentrations ranging from 10-1000 nM did not mobilize intracellular calcium in human ciliary muscle cells. Fluprostenol, a FP receptor agonist linked to intracellular calcium mobilization pathway, mobilized calcium. The inability of unoprostone isopropyl or the metabolite to mobilize intracellular calcium suggests that these compounds have no affinity for EP 1  or FP or TP receptors. These receptors are linked to phospholipase C pathway, stimulation of which results in the mobilization of intracellulaur calcium.  
       CONCLUSIONS  
       [0134]    The results of the studies demonstrated that unoprostone isopropyl or the metabolite does not bind to PG receptor sites.  
         [0135]    In addition to the above Examples 2 and 3, Goth et al, Japanese Journal Ophthalmol, 36: 236-245 (1994), investigated the agonistic activity and affinity of unoprostone (the free acid form) and PhXA34 (also in the free acid form). PhXA34 is an epimeric mixture of 15R and 15S compounds thereby including latanoprost and its 15S-epimer. PhXA34 exhibited ½ the agonistic activity of PGF2α to PGF2α receptors, as determined from contraction of cat iris sphincter, while unoprostone&#39;s agonistic activity was only {fraction (1/1600)} of that of PGF 2α . Binding inhibition studies showed that PhXA34 strongly inhibited [ 3 H] PGF2α binding using boine corpus luteum which has PGF 2α  receptors while the binding inhibitory activity of unoprostone was infinitely weaker than that of PGF 2α  (&lt;&lt;{fraction (1/280)} of PGF 2α )  
         [0136]    The terminology “causing less pigmentation than latanoprost” means over the same treatment time period of at least six months using a clinically approved dosage of once or twice per day, that the compound used in accordance with the present invention causes less irridic pigmentation in comparable irides and/or causes a reduced frequency of pigmentation in a patient population.  
         [0137]    The compounds usable in the present invention are at least five times less potent than latanoprost in stimulating the FP receptor as determined by the test of Example 2 herein. Preferably, the usable compounds are at least about ten times less potent than latanoprost regarding stimulation of the FP receptor. Most preferably, the usable compounds also are those exhibiting virtually no stimulation activity on the EP 1 , EP 2 , EP 3 , TP and IP/DP receptors.  
         [0138]    Variations of the invention will be apparent to the skilled artisan.