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The structure and configuration of an antibiotic, ikarugamycin, have been established to be 1e on the basis of chemical reactions, especially of oxidative degradation. It is suggested that the as-hydrindacene skeleton arises biogenetically via an intramolecular Diels-Alder reaction.

The four 3,4-cis-stereoisomers of dimethyl dl-3-ethyl-4-methyl-1,2-cyclopentanedicarboxylates (1a, 1b, 1c, and 1d) have been synthesized and their configurations established. A comparison of the spectral data and the GLC behaviors has shown that the corresponding ester, one of the key degradation products of ikarugamycin, has the r-1, t-2, c-3, c-4-configuration (1a). The r-1, t-2, c-3, t-4-stereoisomer (1f) has also been prepared.

The five trimethyl dl-3-methoxycarbonylmethyl-1,2,4-cyclopentanetricarboxylates have been synthesized and their configurations determined. A comparison of their spectral properties with those of the corresponding ester obtained from ikarugamycin indicates that the latter has a cis, trans, trans configuration.