Rogioldiol A, a new obtusane diterpene, and rogiolal, a degraded derivative, of the red seaweed Laurencia microcladia from II rogiolo along the coast of tuscany: A Synergism in Structural Elucidation

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AbstractThe structure of rogioldiol A ((−)‐1), isolated from the red seaweed Laurencia microcladia, was determined. Employing the exciton‐coupling technique for rogioldiol A p‐bromobenzoate (2), the absolute configuration at C(9) of (−)‐1 was assigned, and, together with extensive NMR experiments, the absolute configuration at C(10) and preferred conformations of (−)‐1 were determined. The absolute configuration of the hetero‐substituted cyclohexane ring was deduced in analogy from the X‐ray structure of 4, a derivative of the aldehyde 3, which was isolated from the same seaweed and is believed to be a degradation product of (−)‐1.