METHODS FOR THE SYNTHESIS OF 9-CIS RETINOIDS AND THEIR NOVEL INTERMEDIATES

Abstract: Methods for the synthesis of 9-cis retinoids, novel intermediates and methods for the synthesis of cyclohexadienyne nitriles and 9-cis alkyl cisoid nitriles, as well as 9-cis retinoids made using such methods are provided.

Description: METHODS FOR THE SYNTHESIS OF 9-CIS RETINOIDS AND THEIR NOVEL INTERMEDIATES Field of the Invention The present invention relates to the synthesis of 9-cis retinoid compounds, and in particular to the synthesis of 9-cis retinoic acid and related compounds, as well as to their novel intermediates. Background of the Invention The role of retinoids such as all-trans retinoic acid, 13 -cis retinoic acid and synthetic retinoic acid analogs in mediating cell growth and differentiation has generated interest in their pharmacological utility for controlling the treatment of dermatological diseases, such as psoriasis and acne, as well as oncological applications such as chemotherapy and chemoprevention. Significant advances in elucidating the molecular basis of retinoid action now offer the potential for designing retinoid compounds with improved therapeutic indices. To date, several receptors for retinoic acid have been identified. These receptors are members of a superfamily of intracellular receptors which function as ligand dependent transcription factors. At present, these receptors have been classified into two subfamilies, the retinoic acid receptors (RARs) and retinoid X receptors (RXRs). The classification of these subfamilies is based primarily on differences in amino acid structure, responsiveness to different naturally occurring and synthetic retinoids, and ability to modulate expression of different target genes. Each RAR and RXR subfamily has three distinct isoforms designated RARα, RARβ and RARγ, and RXRα, RXRβ and RXRγ. The discovery of multiple retinoid receptors raises questions of the functional properties of the distinct subfamilies and their isoforms. Recently, it has been discovered that 9-cis RA, and other retinoids having a 9-10 cis olefin stereochemisty, are capable of binding to and modulating gene expression via the RARs and RXRs. Heyman et al., Cell, 68:397 (1992). However, to date, the art has only provided low yield, non-selective, high cost methods of making such compounds. For example, the literature has provided non-selective means of generating 9-10 cis olefin retinoids, see e.g., Robson et al., J. Am. Chem. Soc. 77:4111 (1955), Matsui et al., I Viatmino 4: 178 (1958), German Patent No. DE1068719, and Aurell et al., Tetrahedron Lett.. 31:5791 (1990), as well as methods for the stereoselective preparation of the 13-14 olefin bond, see e ^ g . , Pattenden et al., J. Chem. Soc. (C ). 1984 (1968) and Mayer et al., Experientia. 34:1105 (1978). Further, Ernst et al. J. Ore. Chem.. 52:398 (1987) provides methods for the preparation of alkyl- and trimethylsilyl-substituted retinoids via conjugate addition of cuprates to acetylenic esters, which use an excessive number of steps, and importantly, the oxidation of an allylic alcohol to an aldehyde, thereby destroying the integrity of any 9-10 cis olefin bonds present in the resulting retinoids. Accordingly, it would be desirable to prepare retinoid compounds having the 9-10 olefin bond in the cis configuration in a selective, low cost manner. Summary of the Invention The present invention provides methods for the synthesis of 9-cis retinoids, preferably, 9-cis retinoic acid in a selective, low-cost manner. In particular, the present invention provides a method for producing a 9-cis retinoid comprising (a) reducing a cyclohexenyl ketone in the presence of base to form a cyclohexadienyne, (b) condensing the cyclohexadienyne with an electrophilic nitrile source to form a cyclohexadienyne nitrile, (c) adding an alkyl group, in a 1,4 conjugate fashion, to the cyclohexadienyne nitrile to form a cyclohexatriene nitrile, (d) reducing the cyclohexatriene nitrile to the corresponding cyclohexatriene aldehyde, and (e) extending the cyclohexatriene aldehyde with a carbanion equivalent formed by the addition of a base to a phosphonate or phosphine salt to form a reaction product comprising a mixture of retinoid ester stereoisomers wherein the olefin bond between carbons 9-10 is in the cis configuration, and the olefin bonds between carbons 1 1-12, and 13-14 can be in either the trans or cis configuration. Thereafter, the retinoid esters can be hydrolyzed to yield a mixture of retinoic acid stereoisomers, which in turn can be separated to provide individual retinoic acid stereoisomers, preferably, 9-cis retinoic acid. Also provided, is a method for producing a 9-cis retinoid comprising (a) reducing a cyclohexenyl ketone in the presence of base and an electrophilic nitrile source to form a cyclohexadienyne nitrile, (b) adding an alkyl group, in a 1,4 conjugate fashion, to the cyclohexadienyne nitrile to form a cyclohexatriene nitrile, (c) reducing the cyclohexatriene nitrile to the corresponding cyclohexatriene aldehyde, and (d) extending the cyclohexatriene aldehyde with a carbanion equivalent formed by the addition of a base to a phosphonate or phosphine salt to form a reaction product comprising a mixture of retinoid ester stereoisomers wherein the olefin bond between carbons 9-10 is in the cis configuration, and the olefin bonds between carbons 11-12, and 13-14 can be in either the trans or cis configuration. In addition, the present invention provides a method for producing a cyclohexadienyne nitrile olefin comprising reducing a cyclohexenyl ketone in the presence of base and an electrophilic nitrile source to form a cyclohexadienyne nitrile. Further, the present invention provides a method for producing a 9-cis alkyl cisoid nitrile comprising (a) condensing a cyclohexadienyne with an electrophilic nitrile source to form a cyclohexadienyne nitrile, and (b) adding an alkyl group, in a 1,4 conjugate fashion, to the cyclohexadienyne to form a 9-cis alkyl cisoid nitrile, wherein the 9-10 olefin bond is in the CM configuration. Further yet, the present invention provides a 9-cis retinoid made according to the method described above. Preferably such 9-cis retinoid comprises 9-cis retinoic acid, 9,11- dicis retinoic acid, 9, 13 -dicis retinoic acid and 9,11,13 -tricis retinoic acid . These and various other advantages and features of novelty which characterize the invention are pointed out with particularity in the claims annexed hereto and forming a part hereof. However, for a better understanding of the invention, its advantages, and objects obtained by its use, reference should be had to the accompanying drawings and descriptive matter, in which there is illustrated and described preferred embodiments of the invention. Detailed Description of Embodiments of the Invention In accordance with a first aspect of the present invention, we have developed a method to synthesize retinoids. The sequence of steps for this method is shown below. Rl .R 2 „CN (One pot reaction) -78°C to 25°C R Li, Cul THF, -78° 1. KOH, EtOH 70°C In the above process sequences, R 1 and R 2 each can independently represent hydrogen or a lower straight chain or branched alkyl having 1-5 carbon atoms; R 3 represents hydrogen or a lower branched or straight chain alkyl, alkene or alkyne having 1 -6 carbon atoms; R 4 and R 5 each can independently represent hydrogen or a lower branched or straight chain alkyl, alkene, aryl or aralkyl having 1-12 carbon atoms; R 6 represents a lower straight chain or branched alkyl, alkene or alkyne having 1-5 carbon atoms; R 7 represents hydrogen or a pharmaceutically acceptable salt; and the dashed lines in the structures between carbons 11-12, and 13-14, depict olefin bonds ' that can be in either the trans or cis configuration. As used in this disclosure, pharmaceutically acceptable salts include, but are not limited to pyridine, ammonium, piperazine, diethylamine, nicotinamide, formic, urea, sodium, potassium, calcium, magnesium, zinc, lithium, methylamino, triethylamino, dimethylamino, and tris(hydoxymethyl)aminomethane. Additional pharmaceutically acceptable salts are known to those skilled in the art. The process sequence of the method begins with the reduction of a cyclohexenyl ketone 1, such as β-ionone (available from Aldrich Chemical, Milwaukee, WI), in presence of a base, such as lithium diisopropylamide (LDA), and a chlorodiphosphate, such as diethyl chlorophosphate, to form a cyclohexadienyne 2, such as 4-(l-[2,6,6-trimethylcyclohexen-l- yl])-(but-3-ene-l-yne). In addition to LDA as a base, which is preferred, other non-limiting examples of bases useful in this step of the method of the present invention include sodium hydride (NaH), potassium hydride (KH), n-butyl lithium (n-BuLi), s-butyl lithium (s-BuLi), t- butyl lithium (t-BuLi), sodium amide (NaNH 2 ), and lithium, potassium or sodium hexamethyl disylazide. The second step consists of the condensation of the cyclohexadienyne 2 to a cyclohexadienyne nitrile 3, such as 5-(l-[2,6,6-trimethyl-l-cyclohexen-l-yl])-pent-2-yn-4- enenitrile, utilizing an electrophilic nitrile source, such as phenyl cyanate or cyanogen bromide in the presence of base. The third step of this sequence involves the addition of an alkyl group, in a 1,4 conjugate fashion, to cyclohexadienyne nitrile 3 to form an essentially pure cyclohexatriene nitrile 4, such as (2Z,4E)-3-methyl-5-(l-[2,6,6-trimethyl-l-cyclohexen-l-yl])-2,4- pentadienitrile with the 9-10 double bond in the cis configuration. In this regard, the addition of the alkyl group according to this aspect of the method can be accomplished using a number of techniques and methods well known to those of skill in the art, but preferably the addition reaction is accomplished in nonpolar solvents, most preferably in hexanes or heptane. In the fourth step, the cyclohexatriene nitrile 4 is reduced to the corresponding cyclohexatriene aldehyde 5 ((2Z,4E)-3-methyl-5-(l-[2,6,6-trimethyl-l-cyclohexen-l-yl])-2,4- pentadienenal) via a standard DLBAL (diisobutyl aluminum hydride) reduction in hexanes. The fifth step of the sequence involves the extension of the cyclohexatriene aldehyde 5 with a carbanion equivalent formed by the addition of a base (e.g., n-BuLi) to a phosphonate, such as diethyl-3-ethoxycarbonyl-2-methylprop-2-enyl phosphonate, or a phosphine salt (e.g. triphenyl phosphine) to yield a mixture of stereoisomers of retinoates (retinoid esters) 6, including, primarily ethyl-3,7-dimethyl-9-(2,6,6-trimethyl-l-cyclohexen-l- yl)-2-trø«s-4-tra«5-6-cw-8-trøH5-nonatetraenoate. In this regard, the retinoate stereoisomers 6 display over a 15: 1 prevalence of the 13-14 olefin bond in the trans versus cis configuration. Nonlimiting examples of bases useful in this aspect of the method of the present invention include sodium hydride (NaH), potassium hydride (KH), n-butyl lithium (n- BuLi), s-butyl lithium (s-BuLi), t-butyl lithium (t-BuLi), and sodium amide (NaNH,), in the presence of DMPU. The sixth and final step in the process involves the hydrolysis of retinoates 6 with aqueous methanolic hydroxide (MeOH/ KOH) to give retinoic acid isomers 7. Examples of retinoid isomers 7 include, without limitation, the primary component, 3,7-dimethyl-9- (2,6,6-trimethyl- 1 -cy ohexenyl)-2-trø«s-4-trørø-6-cz ' s-8-trø«s-nona-tetraenoic acid {9-cis retinoic acid), and detectable amounts of 3,7-dimethyl-9-(2,6,6-trimethyl-l-cyclohexenyl)-2- c/s-4-trø«.?-6-c/s-8-trø«s-nona-tetraenoic acid (9,13 dicis retinoic acid) and 3,7-dimethyl-9- (2,6,6-trimethyl-l-cyclohexenyl)-2-trα«5-4-c/5-6-c/5-8-trαn5-nona-tetraenoic acid (9,11 dicis retinoic acid). After hydrolysis, a desired retinoic acid isomer 7 can be selectively crystallized from the aqueous methanolic hydroxide solution, or alternatively purified by semi preparative reverse-phase (ODS) high performance liquid chromatography (HPLC). It will be understood by those skilled in the art that certain modifications can be made to the above-described methods that remain within the scope to the present invention. For example, steps one and two (i.e. the condensation of cyclohexadienyne 2) can be combined into a one step, one pot, reaction, by quenching reduced cyclohexenyl ketone 1 with a lithium anion and an electophilic nitrile source, such as phenyl cyanate in the presence of base, instead of with water in the presence of base, to directly yield cyclohexadienyne nitrile 3 Furthermore, it will also be understood by those skilled in the art that the synthesis of the present invention can have broader application beyond the synthesis of the retinoids shown above. For example, the respective condensation and addition of steps two and three can be used to form a variety alkyl cisoid nitriles and their derivatives (e.g., amines, acids, aldehydes, esters) with the 9-10 olefin bond selectively produced in the cis configuration. The synthesis methods described above provide a number of advantages over those currently available, including, importantly, cost. In this regard, the methods of the present invention utilizes commercially inexpensive and readily available starting materials such as β- ionone versus more typical starting materials utilized in existing methodologies, such as β- cyclocitral, which are at least twenty to forty times more expensive on average than the starting materials utilized in the methods of the present invention. In addition, the third step in the synthesis method (i.e. addition of the alkyl group, in a 1,4 conjugate fashion, to the cyclohexadienyne nitrile 3 to form the cyclohexatriene nitrile 4) allows for the selective introduction of the 9-10 double bond in the cis configuration, as well as the ability to place a wide variety of substituents, such as an alkyl, alkene, aryl, aralkyl etc., at carbon number 9. Further, the reagents used throughout the method are standard, readily available and inexpensive organic or inorganic chemicals with no hazardous risks reported. The invention will be further illustrated by reference to the following non-limiting Example. EXAMPLE 1 Synthesis of the retinoids of the present invention are exemplified by the following synthesis scheme for 9-cis retinoic acid. 4-( 1 -\2.6.6-Trimethylcvclohexen- 1 -yl] V (but-3 -ene- 1 -vne'l 2 : The intermediate 4-(l-[2,6,6-trimethylcyclohexen-l-yl])-(but-3-ene-l-yne) 2 was prepared from β-ionone 1 (available from Aldrich Chemicals Inc.) according to the procedures disclosed in E.I. Negishi et al., J. Org. Chem.. 45:2526 (1980), the disclosure of which is herein incorporated by reference. 5-(2.6.6-Trimethyl- 1 -cyclohexen- 1 -yl)-pent-2-yn-4-enenitrile 3 : A 100 mL flame dried flask was charged with the intermediate 4-( 1 -[2,6,6- trimethylcyclohexen-l-yl])-(but-3-ene-l-yne) 2 (1.045 g, 6.0 mmol) in tetrahydrofuran (THF) (30 mL) and cooled to -78°C. A solution of n-BuLi in hexanes (2.25 M; 2.75 mL, 6.15 mmol) was slowly added and the slightly dark mixture was stirred for 10 min. Phenyl cyanate (prepared from phenol and cyanogen bromide according to a procedure of R.E. Murray et al., Synthesis, 150 (1980), the disclosure of which is herein incorporated by reference) (750 μL, 6.6 mmol) was introduced and the mixture allowed to warm to room temperature (e.g., approximately 20-25°C). Sodium hydroxide (2 mL of 6 N solution) was added and the mixture extracted with ethyl acetate (50 mL). The organic layer was further washed with NaOH (2 x 10 mL), water (3 x 10 ml) and brine (2 x 10 mL), dried over MgSO4 and the solvents evaporated. The residue obtained was virtually pure (by TLC) and was filtered through a short pad of silica gel using hexanes as eluent in order to remove some baseline materials. The solvent was evaporated to give 1.088 g (91% yield) of a slightly yellow oil. Rf 0.75 (hexanes), IR (neat) 2933, 2320, 2251 (CN), 1590 cm" 1 ; 1H NMR (CDCI3) δ 7.11 (d, J = 16.4 Hz, 1 H), 5.54 (d, J = 16.4 Hz, 1 H), 2.07 (t, J = 4.0 Hz, 2 H), 1.76 (s, 3 H), 1.60 (m, 2 H), 1.46 (m, 2 H), 1.04 (s, 6 H). (2Z.4E)-3-Methyl-5-(2.6.6-trimethyl-l-cvclohexen-l-ylV2.4-pentadienitrile. 4: A 50 mL flame-dried round bottomed flask was charged with anhydrous copper iodide (1.09 g, 5.70 mmol) and THF (20 ml) and cooled to 0°C. A solution of methyl lithium (4.28 mL of a 1.4 M solution in Et2θ) was slowly added over a 10 min. period until the solution became clear and colorless. The cuprate solution was cooled at -78°C using a dry ice-acetone bath, and a solution of 5-(2,6,6-trimethyl-l-cyclohexen-l-yl)-pent-2-yn-4- enenitrile 3 (544 mg, 2.73 mmol), in THF (10 mL), was added dropwise. See e.g.. H. Westmijze et al., Tetrahedron letters, 3327 (1979), and Synthesis, 454 (1978), the disclosures of which are herein incorporated by reference. The mixture was stirred at this temperature for 45 minutes, and a saturated ammonium chloride solution (10 mL) was added. The reaction mixture was then allowed to warm to room temperature. EtOAc (50 mL) was added and the mixture was washed with 2% NaOH (2 x 10 mL), followed by washings with saturated NH4CI (2 x 10 mL) , water (2 x 10 mL) and brine (2 x 10 mL). The organic layers were dried over MgSO4 and the solvents evaporated. The residue obtained was virtually pure (by TLC) and was filtered through a short pad of silica gel using hexanes:EtOAc (9:1) as eluent in order to remove some baseline materials. The solvent was evaporated to give 538 mg (92% yield) of a slightly yellow-orange oil. Ry0.75 (hexanes:EtOAc (9: 1)), IR (neat) 2933, 2250 (CN), 1590 cm "1 ; 1H NMR (CDCI3) δ 6.70 (d, J = 16 Hz, 1 H), 6.59 (d, J = 16.4 Hz, 1 H), 5.09 (s (1 H), 2.06 (s 3 H), 2.07 (t, J = 4.0 Hz, 2 H), 1.75 (s, 3 H), 1.62 (m, 2 H), 1.47 (m, 2 H), 1.04 (s, 6 H). (2Z.4EV3-Methyl-5-(2.6.6-trimethyl-l-cvclohexen-l-ylV2.4-pentadienenal 5: A 25 mL flame-dried round-bottomed flask was charged with (2Z,4E)-2,4- pentadienitrile-3-methyl-5-(2,6,6-trimethyl-l-cyclohexen-l-yl) 4 (94.2 mg, 0.438 mmol) and hexanes (5.0 mL) and cooled to -78°C. Diisobutyl aluminum hydride (480 μL of a 1.0 M solution in hexanes, 0.480 mmol) was added dropwise at such a rate that the internal reaction temperature did not exceed -70°C. The mixture was stirred for 5 min., and a thin- layer chromotography (TLC) analysis (hexanes :EtO Ac (9:1)) indicated the reaction was complete (Starting material R/0.75; product R/0.70). A saturated solution of Rochelle salt (1.0 mL) was added, and the mixture warmed to room temperature. EtOAc (10 mL) was added and the mixture washed using water (2 x 10 mL) and brine (2 x 10 mL). The organic layers were dried over MgSO4 and the solvents evaporated. The residue obtained was virtually pure (by TLC), 90.5 mg, 95% yield; IR (neat): 2958, 2928, 2866, 1668 (C=O), 1614 (C=C) cm" 1 ; 1H MR (CDCI3; 400 MHz) δ (ppm): 10.16 (d , J = 8.0 Hz, CHO), 7.16 (d , J = 16.0 Hz, vinyl-CH, trans), 6.63 (d , J = 16.0 Hz, vinyl-CH, trans), 5.88 (d, J = 8.0 Hz, 1H, CH-CHO), 2.69 (s, 2 H, ring), 2.14 (s, 3 H, -C-(CH3)=CH-CHO, cis), 1.80 (s, 3 H, CH3, ring), 1.11 (s, 6 H, gem- 2x CH3). Ethyl-3.7-dimethyl-9-(2.6.6-trimethyl- 1 -cvclohexen- 1 -y\)-2-trans-4-trans-6-cis-8-tram- nonatetraenoate 6 A solution of diethyl-3-ethoxycarbonyl-2-methylprop-2-enylphosphonate (354 mg, 1.34 mmol) in anhydrous THF (5.0 mL) was cooled to 0°C and added with anhydrous DMPU (0.5 mL) and «-BuLi in hexanes (0.56 mL of 2.35 M solution, 1.33 mmol). The mixture was stirred at this temperature for 20 minutes, then cooled to -78°C. A solution of (2Z,4E)-3-methyl-5-(2,6,6-trimethyl-l-cyclohexen-l-yl)-2,4-pentadienenal 5 (241 mg, 1.115 mmol) in THF (3.0 mL) was slowly added and the reaction mixture stirred at -78°C for an additional 60 min. The mixture was allowed to warm to 0°C as the reaction went to completion, as monitored by TLC. A saturated solution of ammonium chloride (5 mL) was added, and the mixture extracted using EtOAc (3 xlO mL). The organic layer was washed with water (2 x 5 mL) and brine (10 mL), dried over MgSO4 and concentrated. The residue was purified on a short silica gel chromotography (sgc) column to give 296 mg (78% yield) ofthe desired ester in a -15:1 ratio of \3-trans: \3-cis isomers. IR (neat): 2928, 1709 cm ~ l; 1H NMR (CDCI3; 400 MHz) δ (ppm): 7.08 (dd, J = 15, 11.3 Hz, 1 H), 6.65 (d, J = 16 Hz, 1 H), 6.29 (d, J = 15 Hz, 1 H), 6.23 (d, J = 15 Hz, 1 H), 6.06 (d, J = 11.3 Hz, 1 H), 4.17 (m, J=7 Hz, 2 H), 2.7 (s, 2 H), 2.33 (s, 3 H), 2.03 (s 3 H), 1.82 (s, 3 H) 1.29 (t, J = 7 Hz, 3 H), l. l (s, 6 H). 3.7-Dimethyl-9-(2.6.6-trimethyl-l-cvclohexenylV2-trαw. y -4-trgw -6-c; -8-t 5-nona- tetraenoic acid 7 A solution of ethyl-3,7-dimethyl-9-(2,6,6-trimethyl-l-cyclohexen-l-yl)-2-trα«5-4- tra/75-6-cw-8-trα«5-nonatetraenoate 6 (275 mg, 8.25 mmol) in ethanol (10 mL) was treated with 1 N KOH (10 mL) at 70°C for 3 hours, cooled to room temperature, acidified with 10% (v:v) HC1, and extracted with EtOAc (2 x 20 mL). The organic layer was washed with water (2 x 5 mL) and brine (2 x 5 mL), dried over MgSO4 and the solvent was evaporated. The residue was recrystallized (2 times) by dissolving it in a minimum volume of a 9: 1 mixture of ethanol: water (-20 ml per gram of material). The desired 9-cis retinoic acid was thus obtained in a highly pure form (by 1H NMR) as light yellow solid, yield 85%; mp. 188- 190°C; IR (KBr, cm" 1 ) 2914, 1670, 1583; 1H NMR (CDCI3; 400 MHz): δ (ppm) 7.20 (dd, J = 15.0 Hz, 1 H), 6.65 (d, J = 16.0 Hz, 1 H), 6.28 (d, J = 16.0 Hz, 1 H), 6.25 (d, J = 15.0 Hz, 1 H), 6.06 (d, J = 11.0 Hz, 1 H), 5.80 (s, 1 H), 2.35 (s, 3 H), 2.05 (t, J = 6.6 Hz, 2 H), 2.01 (s, 3 H), 1.75 (s, 3 H), 1.64 (m, 2 H), 1.49 (m, 2 H), 1.04 (s, 6 H). While in accordance with the patent statutes, description ofthe preferred embodiments and processing conditions have been provided, the scope ofthe invention is not to be limited thereto or thereby. Various modifications and alterations ofthe present invention will be apparent to those skilled in the art without departing from the scope and spirit ofthe present invention. Consequently, for an understanding ofthe scope ofthe present invention, reference is made to the following claims.

Claims: What is claimed is: 1. A method for producing a 9-cis retinoid comprising: (a) reducing a cyclohexenyl ketone in the presence of base to form a cyclohexadienyne ofthe formula: (b) condensing the cyclohexadienyne with an electrophilic nitrile source to form a cyclohexadienyne nitrile; (c) adding an alkyl, alkene, aryl or aralkyl group, in a 1,4 conjugate fashion, to the cyclohexadienyne nitrile to form a cyclohexatriene nitrile ofthe formula: (d) reducing the cyclohexatriene nitrile to the corresponding cyclohexatriene aldehyde; and (e) extending the cyclohexatriene aldehyde with a carbanion equivalent formed by the addition of a base to a phosphonate or phosphine salt to form a reaction product comprising a mixture of retinoid ester stereoisomers having the general formula: wherein, R 1 and R 2 each can independently represent hydrogen or a lower straight chain or branched alkyl having 1-5 carbon atoms; R 3 represents hydrogen or a lower branched or straight chain alkyl, alkene or alkyne having 1-6 carbon atoms; R 4 and R' each can independently represent hydrogen or a lower branched or straight chain alkyl, alkene, aryl or aralkyl having 1-12 carbon atoms; R 6 represents a lower straight chain or branched alkyl, alkene or alkyne having 1 -5 carbon atoms; and the dashed lines in the structures between carbons 11-12, and 13-14, depict olefin bonds that can be in either the trans or cis configuration. 2. A method according to claim 1, further comprising, after the extending step, hydrolyzing the reaction product with an aqueous methanolic hydroxide to form a mixture of retinoid stereoisomers. 3. A method according to claim 2, further comprising, after the hydrolyzing step, isolating a retinoid stereoisomer having the general formula: wherein R 1 to R 5 have the meaning specified in claim 1 , R 7 represents hydrogen or a pharmaceutically acceptable salt and the 11-12 and 13-14 olefin bonds are in either the tram or cis configuration. 4. A method according to claim 1, wherein the electrophilic nitrile source comprises phenyl cyanate or cyanogen bromide. 5. A method according to claim 1, wherein the phosphonate or phosphine salt comprises diethyl-3-ethoxycarbonyl-2-methylprop-2-enylphosphonate. 6. A method according to claim 3, wherein the 9-cis retinoid is selected from the group consisting of 3, 7-dimethyl-9-(2,6,6-trimethyl-l-cyclohexenyl)-2-tra -4-trαrø-6-CΛS'-8-trø '- nonatetraenoic acid, 3,7-dimethyl-9-(2,6,6-trimethyl-l-cyclohexenyl)-2-c/5-4-trαw5 , -6-c/5-8- trøws-nonatetraenoic acid, and 3,7-dimethyl-9-(2,6,6-trimethyl-l-cyclohexenyl)-2-/ra«.y-4- c7 ' .v-6-c/ ' .y-8-trarcs-nonatetraenoic acid. 7. A method for producing a 9-cis retinoid comprising: (a) reducing a cyclohexenyl ketone in the presence of base and an electrophilic nitrile source to form a cyclohexadienyne nitrile ofthe formula: (b) adding an alkyl, alkene, aryl or aralkyl group, in a 1,4 conjugate fashion, to the cyclohexadienyne nitrile to form a cyclohexatriene nitrile; (c) reducing the cyclohexatriene nitrile to the corresponding cyclohexatriene aldehyde; and (d) extending the cyclohexatriene aldehyde with a carbanion equivalent formed by the addition of a base to a phosphonate or phosphine salt to form a reaction product comprising a mixture of retinoid ester stereoisomers having the general formula: wherein, R 1 and R 2 each can independently represent hydrogen or a lower straight chain or branched alkyl having 1-5 carbon atoms; R 3 represents hydrogen or a lower branched or straight chain alkyl, alkene or alkyne having 1-6 carbon atoms; R 4 and R 5 each can independently represent hydrogen or a lower branched or straight chain alkyl, alkene, aryl or aralkyl having 1-12 carbon atoms; R 6 represents a lower straight chain or branched alkyl, alkene or alkyne having 1-5 carbon atoms; and the dashed lines in the structures between carbons 11-12, and 13-14, depict olefin bonds that can be in either the trans or cis configuration. 8. A method according to claim 7, further comprising, after the extending step, hydrolyzing the reaction product with an aqueous methanolic hydroxide to form a mixture of retinoid stereoisomers. 9. A method according to claim 8, further comprising, after the hydrolyzing step, isolating a retinoid stereoisomer having the general formula: wherein R 1 to R 5 have the meaning specified in claim 7, R 7 represents hydrogen or a pharmaceutically acceptable salt and the 11-12 and 13-14 olefin bonds are in either the trans or cis configuration. 10. A method according to claim 9, wherein the 9-cis retinoid is selected from the group consisting of 3,7-dimethyl-9-(2,6,6-trimethyl-l-cyclohexenyl)-2-tr-w.v-4-tra/J5-6-cz ' 5-8-tra«5- nonatetraenoic acid, 3 , 7-dimethyl-9-(2, 6, 6-trimethyl- 1 -cyclohexenyl)-2-c/ ' s-4-tr< s-6-c s-8- trøw-nonatetraenoic acid, and 3, 7-dimethyl-9-(2, 6, 6-trimethyl- 1 -cyclohexenyl)-2-trø«s-4- c/s-6-c7.y-8-tra/M-nonatetraenoic acid. 11. A method for producing a cyclohexadienyne nitrile olefin comprising reducing a cyclohexenyl ketone in the presence of base and an electrophilic nitrile source to form a cyclohexadienyne nitrile ofthe formula: wherein, R 1 and R 2 each can independently represent hydrogen or a lower straight chain or branched alkyl having 1-5 carbon atoms, and R 3 represents hydrogen or a lower branched or straight chain alkyl, alkene or alkyne having 1-6 carbon atoms. 12. A method for producing a 9-cis alkyl cisoid nitrile comprising: (a) condensing a cyclohexadienyne with an electrophilic nitrile source to form a cyclohexadienyne nitrile, and (b) adding an alkyl, alkene, aryl or aralkyl group, in a 1,4 conjugate fashion, to the cyclohexadienyne to form a 9-cis alkyl cisoid nitrile ofthe formula: wherein, R 1 and R 2 each can independently represent hydrogen or a lower straight chain or branched alkyl having 1-5 carbon atoms, R 3 represents hydrogen or a lower branched or straight chain alkyl, alkene or alkyne having 1-6 carbon atoms; R 4 represents hydrogen or a lower branched or straight chain alkyl, alkene, aryl or aralkyl having 1-6 carbon, and the 9-10 bond is in the cis configuration. 13. A 9-cz5 retinoid made according to the method of claim 1. 14. A 9-cis retinoid according to claim 13, selected from the group consisting of 3,7- dimethyl-9-(2, 6, 6-trimethyl- 1 -cyclohexenyl)-2-t> ws-4-trøm-6-c7s-8-trø«s-nonatetraenoic acid, 3,7-dimethyl-9-(2,6,6-trimethyl-l-cyclohexenyl)-2-cw-4-trβf«5-6-c/ό'-8-rrύr«5- nonatetraenoic acid, and 3,7-dimethyl-9-(2,6,6-trimethyl-l-cyclohexenyl)-2-trø -4-c7S-6- cw-8-trøΛ7s-nonatetraenoic acid. 15. 5-(2,6,6-Trimethyl- 1 -cyclohexen- 1 -yl)-pent-2-yn-4-enenitrile.

Inventors: BENNANI YOUSSEF L, BENNANI, YOUSSEF, L.
Applicants: LIGAND PHARM INC, LIGAND PHARMACEUTICALS INCORPORATED
Application year: 1995
Main classification: C07C403
IPC codes: C07C253, C07C255, C07C403