合成路线1

The reaction of tetrahydrofuran (I) with HBr gives 4-bromobutanol (II), which is oxidized with NaOCl and TEMPO to yield the aldehyde (III). The reaction of (III) with ethyleneglycol and Ts-OH provides the cyclic ketal (IV), which is submitted to a Grignard condensation with diethyl oxalate (V) and Mg to give the alpha-ketoester (VI). The hydrolysis of (VI) with LiOH yields the corresponding alpha-ketoacid (VII), which is submitted to a stereoselective amination with ammonia and phenylalanine dehydrogenase to afford 2(S)-amino-5-(1,3-dioxol-2-yl)pentanoic acid (VIII). The reaction of (VIII) with SOCl2 and Me-OH provides 2(S)-amino-5,5-dimethoxypentanoic acid methyl ester (IX). The reaction of L- homocystine (X) with Boc2O gives the N-protected-L-homocystine (XI), which is condensed with pentanoic ester (IX) to yield the dimeric adduct (XII). The cleavage of (XII) with dithiothreitol (DTT) affords the monomeric intermediate (XIII), which is finally cyclized by means of Ms-OH to provide the target pyrido[2,1-b][1,3]thiazepine intermediate (XIV).