Spirobistetrodecamycins A and B: Spontaneous dimeric spiro-fused vinyl cyclobutanes of tetrodecamycin

Spirobistetrodecamycins A and B (1 and 2), tetrodecamycin-derived vinyl cyclobutane dimers, are herein re-ported for the first time. Their structures including absolute configurations were elucidated by extensive spec-troscopic methods, single-crystal X-ray diffraction, and ECD calculations. As a way to provide a rationale for the spontaneous formation of these dimers, the irradiation of tetrodecamycin has been carried out leading to the production of regioisomeric [2 + 2] head-to-head 1 and head-to-tail 2. These two compounds showed no anti-bacterial activity against Escherichia coli, Micrococcus luteus, and Bacillus subtilis.