In the course of our screening program for novel antimicrobial antibiotics against Pasteurella piscicida, we have isolated new antibiotics, tetrodecamycin (1) and weakly active dihydrotetrodecamycin (2) from a culture broth of a streptomycete. The MICs of 1 were 6.25-12.5μg/ml and 1.56-6.25μg/ml against Gram-positive bacteria and two strains of P.piscicida, respectively. The molecular formula of 1 was determined to be C_<18>H_<22>_O_6 by HRFAB-MS and ^<13>C-NMR spectral data of 1 and acetyl derivative (3). The planar structure of 1 was elucidated by various NMR spectral analyses of 1 and 3, except for an acyl tetronic acid alkyl ether moiety. This moiety was established by comparison of its ^<13>C chemical shifts with those of gregatin B. The IR and UV spectral data of 1 also suggested the presence of the acyl tetronic acid moiety. The structure of 2 was elucidated by comparison with the spectral data of 1. The relative stereochemistry of 2 was determined by X-ray crystallography. The stereochemistry of 1 was as same as 2, because 1 was converted into 2 by catalytic reduction. The absolute stereochemistry was determined by modified Mosher's method applied to secondary alcohol of 1. The structure-activity relationships of the ester derivatives of 1 were also described.
