The synthesis of Ro-31-8959/003 (X) was carried out as follows: Condensation of L-phenylalanine (I) with formaldehyde in concentrated hydrochloric acid gave the tetrahydroisoquinoline (II), which was hydrogenated in 90% acetic acid over rhodium on carbon to yield the decahydroisoquinoline (III) as a mixture of diastereoisomers. Treatment of (III) with benzyl chloroformate in aqueous sodium hydroxide solution gave a mixture of N-protected amino acids which was separated by fractional crystallization of the cyclohexylamine salts to give the (S,S,S)-isomer. Reaction with dicyclohexylcarbodiimide and N-hydroxysuccinimide in dimethoxyethane, followed by treatment of the activated ester with tert-butylamine in dichloromethane and subsequent hydrogenolysis of the benzyloxycarbonyl protecting group gave the decahydroisoquinoline (IV). In the other branch of the synthesis L-phenylalanine was treated with benzyl chloroformate in aqueous sodium hydroxide solution to give the N-protected amino acid. This was converted to the corresponding mixed anhydride with isobutyl chloroformate and N-ethylmorpholine in tetrahydrofuran and immediately reacted with diazomethane in diethyl ether to give the diazomethyl ketone (V). Treatment of (V) with ethereal hydrogen chloride gave the chloromethyl ketone (VI), which on reduction with sodium borohydride in aqueous tetrahydrofuran gave a mixture of diastereoisomeric chlorohydrins. Solvent extraction with boiling n-hexane followed by recrystallization of the less soluble isomer from isopropanol gave pure chlorohydrin (VII), which on treatment with ethanolic potassium hydroxide gave the epoxide (VIII). Condensation of (VIII) with (IV) in ethanol gave the hydroxyethylamine (IX). Hydrogenolysis of (IX) was followed by condensation with N-benzyloxycarbonyl-L-asparagine in tetrahydrofuran in the presence of 1-hydroxybenzotriazole and dicyclohexylcarbodiimide. Hydrogenolysis in ethanol over palladium on charcoal, followed by condensation with quinoline-2-carboxylic acid in tetrahydrofuran in the presence of dicyclohexylcarbodiimide and 1-hydroxybenzotriazole, gave the free base, Ro-31-8959/000. Treatment with methanesulfonic acid in aqueous ethanol then afforded the mesylate salt (X), Ro-31-8959/003.

Various new routes for the large-scale synthesis of Ro-31-8959 have been described: 1) The condensation of N-protected-L-phenylalanine (I) with the Mg salt of malonic acid monoethyl ester (II) gives the keto ester (III), which is enantioselectively reduced with NaBH4 to yield the hydroxy ester (IV). The reaction of (IV) with 2,2-dimethoxypropane (V) by means of p-toluenesulfonic acid affords the oxazolidine (VI), which is hydrolyzed with NaOH in ethanol/water to the corresponding acid (VII). The treatment of (VII) with oxalyl chloride, mercaptopyridine-N-oxide (MPO) and bromotrichloromethane affords the bromomethyloxazolidine (VIII), which, without isolation, is treated with acetic acid to give the N-protected 3(S)-amino-2-bromo-4-phenyl-2(S)-butanol (IX). The reaction of (IX) with KOH in methanol yields the epoxide (X), which is condensed with (3S,4aS,8aS)-N-tert-butyldecahydroisoquinoline-3-carboxamide (XI), yielding the protected condensation product (XII). The deprotection of the amino group of (XII) by hydrogenation with H2 over Pd/C affords the amino derivative (XIII), which is condensed with N-benzyloxycarbonyl-asparagine (XIV) in the usual way, giving the protected peptide (XV). The deprotection of (XV) as before yields compound (XVI), with a free amino group that is finally condensed with quinoline-2-carboxylic acid (XVII) by means of dicyclohexylcarbodiimide and hydroxybenzotriazole.

2) The condensation of N-phthaloyl-L-phenylalaninyl chloride (XVIII) with 1,1,2-tris(trimethylsilyloxy)ethylene (TMS) (XIX) at 90-100 C followed by acidic hydrolysis with HCl gives the acid (XX), which, without isolation, is decarboxylated, yielding 1-hydroxy-3(S)-phthalimido-4-phenyl-2-butanone (XXI). Sequential protection of the OH- group with dihydropyran, reduction of the CO group with NaBH4, mesylation of the resulting OH group with methanesulfonyl chloride and deprotection of the primary OH group gives 2(R)-(methanesulfonyloxy)-4-phenyl-3(S)-phthalimido-1-butanol (XXII). The epoxidation of (XXII) with potassium tert-butoxide yields the epoxide (XXIII), which is condensed with the decahydroisoquinoline (XI) as before, affording the protected condensation product (XXIV). The elimination of the phthalimido group of (XXIV) with methylamine and HCl gives the amino derivative (XIII), already obtained in scheme 16810301a.

3) The condensation of N-(tert-butoxycarbonyl)-L-phenylalaninal (XXV) with 2-(trimethylsilyl)thiazole (XXVI) by means of tetrabutylammonium fluoride gives the thiazole derivative (XXVII), which is cleaved by reaction with methyl iodide (formation of the thiazolium derivative) and treated with NaBH4 and HgCl2 to afford the protected 3(S)-amino-2(S)-hydroxy-4-phenylbutanal (XXVIII). Finally, this compound is reductocondensed with isoquinoline (XI) by means of sodium cyanoborohydride to yield the protected condensation product (XII), already obtained in scheme 16810301a.

4) The selective esterification of 3(S)-azido-4-phenylbutane-1,2(S)-diol (XXIX) with 2,4,6-triiosopropylbenzenesulfonyl chloride (XXX) gives the sulfonate ester (XXXI), which by treatment with KOH is converted to the azido epoxide (XXXII). The condensation of (XXXII) with decahydroisoquinoline (XI) affords the azido condensation product (XXXIII), which is finally hydrogenated with H2 over Pd/C to the amino condensation product (XIII), already obtained in scheme 16810301a. 5) The reaction of (XXIX) with SOCl2 and RuCl3 gives the dioxathiole dioxide (XXXIV), which is condensed with decahydroisoquinoline (XI) to afford the azido condensation product (XXXIII), already obtained.

The intermediate (3R,4S)-4-[N-(tert-butoxycarbonyl)-N-methylamino]-5-phenyl-3-(tert-butyldimethylsilyloxy)pentanoic acid (VII) has been obtained as follows: The condensation of N-(tert-butoxycarbonyl)-L-phenylalanine (I) with the Mg salt of malonic acid monoethyl ester (II) by means of CDI gives the beta-ketoester (III), which is reduced with NaBH4 to yield (3R,4S)-4-(tert-butoxycarbonylamino)-3-hydroxy-5-phenylpentanoic acid ethyl ester (IV). The protection of the OH group of (IV) with Tbdms-Cl and imidazole in DMF affords the silylated ester (V), which is hydrolyzed with NaOH to provide the corresponding carboxylic acid (VI). Finally, this compound is N-methylated by means of Me-I and NaH in THF to obtain the target intermediate (VII).

[14C]-Saquinavir: The cyclization of [ring-14C]-aniline (I) with crotonic aldehyde (II) by means of HCl and acetic anhydride gives labeled 2-methylquinoline (III), which is brominated with Br2 in acetic acid yielding the tribromo derivative (IV). The hydrolysis of (IV) with hot sulfuric acid afforded labeled quinoline-2-carboxylic acid (V), which is finally condensed with Ro-32-0445 (VI) by means of hydroxybenzotriazole (HOBT) and dicyclohexylcarbodiimide (DCC) in THF.

Pentadeuterated saquinavir: The nitration of hexadeuterobenzene (VII) with HNO3/H2SO4 gives pentadeuteronitrobenzene (VIII), which is hydrogenated with deuterium/Pt in D1-methanol yielding heptadeuteroaniline (IX). The cyclization of (IX) with crotonic aldehyde (II) by means of DCI/D2O and acetic anhydride as before affords hexadeuterated quinoline (X), which is brominated with Br2 as before giving the tribromo derivative (XI). The hydrolysis of (XI) with sulfuric acid as before yields the acid (XII), which is finally condensed with Ro-32-0445 (VI) as before.

Tetradeuterated saquinavir: The cyclization of heptadeuteroaniline (IX) with crotonic aldehyde (II) by means of HCl and acetic anhydride as before gives the tetradeuteroquinoline (XIII), which is brominated as described yielding the tribromo derivative (XIV). The hydrolysis of (XIV) with sulfuric acid affords tetradeuterated acid (XV), which is finally condensed with Ro-32-0445 (VI) as indicated.

Tritiated saquinavir: The cyclization of 4-bromoaniline (XVI) with crotonic aldehyde (II) by means of ZnCl2/HCl gives 6-bromo-4-methylquinoline (XVII), which is brominated as before giving tetrabromo derivative (XVIII). The hydrolysis of (XVIII) with sulfuric cid affords 6-bromoquinoline-2-carboxylic acid (XIX), which is condensed with Ro-32-0445 (VI) by means of HOBT and DCC as indicated giving the bromo derivative of saquinavir (XX). Finally, this compound is tritiated with T2 over Pd/C in ethanol.

5)[15N,13C,2H]-Saquinavir: The nitration of [13C6]-benzene (XXI) with [15N]-nitric acid gives the corresponding nitrobenzene (XXII), which is reduced with Sn/HCl to the aniline (XXIII). The cyclization of (XXIII) with crotonic aldehyde (II) by means of ClD/D2O and acetic ahydride yields the tetradeuterated quinoline (XXIV), which is brominated as before givig the tribromo derivative (XXV). The hydrolysis of (XXV) with sulfuric acid as usual affords the [15N,13C6,2H3]-labeled quinoline-2-carboxylic acid (XXVI), which is finally condensed with Ro-32-0445 (VI) by means of HOBT and CDI as indicated.