Triostin A, a cyclic octadepsipeptide, was synthesized with Z–d-Ser[Boc–Ala–MeCys(Bzl)–MeVal]–OH and Z–d-Ser[H–Ala–MeCy(Bzl)–MeVal]–OTce as key intermediates. The synthetic antibiotic was compared with natural triostin A in terms of chromatographic behaviors, NMR spectra, and antimicrobial activity to establish their identity. The NMR data on S,S′-dibenzyldihydrotriostin A showed that this intermediate lacking the disulfide linkage also existed as two conformers in chloroform. This observation excludes the possibility that the conformer equilibrium known to occur with triostin A is a consequence of the reversed chirality of the disulfide bond.

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SynopsisT h e solution polymerization of vinyl acetate w a s curried out in several solvents a t 0 to 100cC, using 2,2'-azobisisobutyronitrile as initiator. For the resulting poly(viny1 alcohol) (PVA), iodinecoloration, 1.2-glycol structure and tacticity were observed. The pentad tacticity of PVA was estimated from its methine carbon spectra by means of '"C-FTNMIi spectrometer. Iodine-coloration ahility of PVA v M d markedly with the type of polymerization solvent and decreased in the following order: phenol > aq. phenol > methyl alcohol ethyl acetate > IIMSO, ethylene carboriiite. T h e syndiotactic fraction in PVA also decreased with polynierimtion solvent in the .same order (ts that of iodine coloration, while 1,2-glycol content of PVA was not almost affected by polymerization solvent except for phenol and aq. phenol. In solution polymerization performed, effect of polymerization temperature on tacticity was less than that of solvent. 15. F.