抄録
Ezomycin complex, produced by a strain of Streptomyces, is a mixture of novel antifungal antibiotics. We have succeeded in the isolation of four components from the complex, ezomycins A_1 (C_<26>H_<38>N_8O_<15>S・H_2O), A_2(C_<19>H_<26>N_6O_<12>・H_2O), B_1(C_<26>H_<39>N_7O_<17>S), B_2(C_<19>H_<27>N_5O_<14>) and disclosed that A_1 and B_1, the main active components, are new peptidyl pyrimidine nucleosides containing L-cystathionine. Quite recently, structural elucidation of A_1 and A_2 was accomplished in the following way. When hydrolyzed with Dowex 50W (H^+), A_1 (I) liberated L-cystathionine and A_2 (II) as main products. This indicates that I is composed of II and L-cystathionine. Acid hydrolysis of II afforded cytosine and ezoaminuroic acid, C_6H_<11>NO_5. On alkaline hydrolysis I was subjected to β-elimination of ezoaminuroic acid moiety, yielding anhydronucleoside A (IV), C_<13>H_<14>N_4O_8, whose carbohydrate moiety accounts for the remaining unknown 8 carbon atoms. Oxidation of I with 2 molar equivalents of NaIO_4, followed by mild acid hydrolysis, gave 1 molar equivalent of glyoxal, lactam-aminohemiacetal (VIII) and nuclebside A (IX), C_<13>H_<17>N_5O_8. On the basis of the physico-chemical evidences of IV, IX and their derivatives, the structures IV and IX were deduced. Accordingly the structure of A_2 was elucidated as II. VIII was reduced by NaBH_4 to give a compound (XI) which produced L-cystathionine sulfoxide and (S)-α-hydroxy-butyrolactone on acid hydrolysis. I was desulfurized with Raney Ni to liberate alanine. From these facts the structure of A_1 was determined to be I as depicted in Scheme 1.
