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Four Novel Diterpenes, Cyanthiwigin A-D (1–4) Have Been Isolated From The Marine Sponge E. Reiswigi And Their Structure Elucidated By Mass And Mainly Nmr Spectra. The Tricarbocyclic Structure Of 1 Was Confirmed By An X-Ray Analysis And Its Absolute Configuration Was Established To Be 4s, 5r, 6s, 9s By The Modified Mosher's Method. The Four Compounds Have The Same Planar Skeleton As Cyanthin But Differ In Their Stereochemistry.
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Green et al. (1992) studied this question.
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