Steric conversion of N-benzoyl-DL-
erythro-β-[2-(5-nitro)-furyl]-serine ethyl ester m.p. 117°, to O-benzoyl-DL-
threo-[2-(5-nitro)-furyl]-serine ethyl ester hydrochloride, m.p. 175° (decomp.), was effected by the application of thionyl chloride, intermediately forming an oxazoline ring and with migration of the benzoyl group from nitrogen to oxygen. The latter compound was used for the attempt in obtaining
threo-type N-acyl derivatives by the application of
p-nitrobenzoyl, 2, 4-dichlorobenzoyl, furoyl, 5-nitrofuroyl, furylacryloyl, and 2-(5-nitro)-furylacryloyl chlorides to the O-benzoyl compound. Since the crystallization of their products was difficult, they were submitted to chromatography through alumina by which the objective compounds could not be obtained and ethyl N-acylamido-β-[2-(5-nitro)-furyl]-acrylates were obtained by the concurrent liberation of benzoic acid. On the other hand, the same reactions with benzoyl,
p-chlorobenzoyl, and cinnamoyl chlorides yielded the corresponding O-benzoyl-N-acyl-DL-
threo-β-[2-(5-nitro)-furyl]-serine ethyl esters in crystalline form. In the case of 2, 4-dichlorobenzoyl chloride, the final product was isolated as O-benzoyl-N-2, 4-dichorobenzoyl-DL-
threo-β-[2-(5-nitro)-furyl]-serine ethyl ester. Chromatography through alumina of N-2, 4-dichlorobenzoyl-DL-
erythro-β-[2-(5-nitro)-furyl]-serine ethyl ester and O-benzoyl-N-2, 4-dichlorobenzoyl-DL-
threo-β-[2-(5-nitro)-furyl]-serine ethyl ester separately yielded identical ethyl N-2, 4-dichlorobenzoyl-β-[2-(5-nitro)-furyl]-acrylate, m.p. 229°, confirmed by ultraviolet absorption spectrum. A large difference in the absorption in the infrared region above 10μ was observed between the
erythro- and
threo-type compounds.
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