Crystal and molecular structure of eupaformonin, a cytotoxic germacranolide from Eupatorium formosanum HAY
- 1 January 1976
- journal article
- research article
- Published by Royal Society of Chemistry (RSC) in Journal of the Chemical Society, Perkin Transactions 2
- No. 5,p. 578-582
- https://doi.org/10.1039/p29760000578
Abstract
Single-crystal X-ray analysis has established the structure and relative stereochemistry of the title compound (I). The absolute configuration follows from the sign of the Cotton effect of then n→π* transition of the α-methylene γ-lactone CC–CO chromophore. Crystals are orthorhombic, space group P212121, a= 14.28(2), b= 11.52(2), c= 9.68(2)Å, Z= 4. The structure was solved by direct phase-determining methods and atomic parameters refined by full-matrix least-squares calculations to R 0.093 over 1 437 reflections from photographic data. The Δ1(10)trans, Δ4cis-cyclodecadiene ring is in a chair, boat conformation with the C(4) and C(10) methyl groups oriented anti. The anomalous relationship between the sign of the measured Cotton effect of the CC–CO chromophore n→π* transition for Δ1(10)trans, Δ4cis germacranolide C(6), C(7)-trans-fused α-methylene γ-lactones and the position and stereochemistry of the lactone ring fusion is discussed with respect to the preferred cyclodecadiene ring conformation.Keywords
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