合成路线1

1) The condensation of S-acetyl-N-(benzyloxycarbonyl)-L-homocysteine (I) with 6-hydroxy-L-norleucine methyl ester (II) by means of 1-[3-(dimethylamino)propyl]-3-ethylcarbodiimide (WSC) and hydroxybenzotriazole (HOBT) in dichloromethane gives the corresponding dipeptide (III), which is oxidized with oxalyl chloride in dichloromethane, yielding the aldehyde (IV). The cyclization of (IV) by means of sodium methoxide and trifluoroacetic acid affords the perhydro-pyridothiazepinone (V), which is deprotected with trimethylsilyl iodide (TMS-I) in dichloromethane to give (VI) with a free amino group (1). The acylation of (VI) with 2(S)-(acetylsulfanyl)-3-phenylpropionic acid (VII) by means of (benzotriazol-1-yloxy)tris(dimethylamino)phosphonium hexafluorophosphate (BOP) in dichloromethane yields the corresponding amide (VIII), which is finally deprotected with NaOH in methanol and treated with HCl. 2) The intermediates S-acetyl-N-(benzyloxycarbonyl)-L-homocysteine (I) and 6-hydroxy-L-norleucine (II) have been obtained as follows: 2a) The protection of 3-aminotetrahydrothiophen-2-one (IX) with N-(benzyloxycarbonyloxy)succinimide gives the expected carbamate (X), which is treated first with KOH and then with acetic anhydride, yielding S-acetyl-N-(benzyloxycarbonyl)-DL-homocysteine (XI). Finally, this compound is submitted to optical resolution with (S)-alpha-methylbenzylamine to afford intermediate (I). 2b) The alkylation of acetamidomalonic acid diethyl ester (XII) with 4-acetoxybutyl bromide (XIII) by means of NaH in DMF gives the alkylated ester (XIV), which by a decarboxylative saponification yields 6-acetoxy-DL-norleucine (XV). Optical resolution of (XV) by means of porcine kidney acylase/LiOH in water affords pure 6-hydroxy-L-norleucine (XVI), which is finally esterified with methanol/HCl to intermediate (II).