1) Condensation of 5-nitrofurfural with glycine ethyl ester, at various temperatures and in different solvents (benzene, ether, ethyl acetate, chloroform, and chlorobenzene), only gave
erythro-3-(5-nitro-2-furyl)-DL-serine ethyl ester.
2) In contrast to the above result, it was found that the reaction gives only
threo-3-(5-nitro-2-furyl)-DL-serine ethyl ester by using a benzene solution containing a catalytic amount of piperidinium acetate, although the yield was poor.
3) Attempting to make better the yield, fourteen kinds of piperidinium salt were used trying this reaction. Among these catalysts, piperidinium 3-(5-nitro-2-furyl)-acrylate gave
threo-3-(5-nitro-2-furyl)-DL-serine ethyl ester hydrochloride in the best yield. In order to estimate the amount of this ester hydrochloride formed, the two melting point curves shown in Fig. 3 and 4, were plotted. Fig. 3 was made by the melting point determination of various mixtures of pure N-benzoyl-
erythro- and pure N-benzoyl-
threo-3-(5-nitro-2-furyl)-DL-serine ethyl ester, and Fig. 4 by the determination of variously benzoylated mixtures derived from a mixture of pure
erythro- and
threo-3-(5-nitro-2-furyl)-DL-serine ethyl ester hydrochloride by direct benzoylation. In this work, the determination of the yield was conditionally accomplished by using Fig. 4.
4) No depression of the melting point occured on fusion of O, N-dibenzoyl compound of the above-mentioned
threo-3-(5-nitro-2-furyl)-DL-serine ethyl ester hydrochloride with the O, N-dibenzoylated product obtained from N-benzoyl-
erythro-3-(5-nitro-2-furyl)-DL-serine ethyl ester through inversion with thionyl chloride.
5) The infrared spectra of N-benzoyl-
erythro- and N-benzoyl-
threo-3-(5-nitro-2-furyl)-DL-serine ethyl ester did not show the regularity like that of ephedrine and chloramphenicol. Similar observations were made with ethyl esters of N-benzoyl-3-phenylserine and N-benzoyl-3-(
p-nitrophenyl) serine.
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