CRYSTAL-STRUCTURE OF A 1 1-COMPLEX OF NATURAL DITERPENOIDS - ABSOLUTE-CONFIGURATIONS AND UNAMBIGUOUS NMR SPECTRAL ASSIGNMENTS OF NEOANGUSTIFOLIN AND EPINODOSINOL/

Diterp-Complex-RA (DCRA), a unique, inseparable, natural hydrogen-bond ed 1:1 complex consisting of a novel diterpenoid neoangustifolin and a known diterpenoid epinodosinol, was isolated from Rabdosia angustifol ia, along with daucosterol and the known diterpenes sodoponin, trichor abdal A, and cirsiliol. The binding mode of the complex and the absolu te configuration of the two substrates were elucidated through X-ray c rystallography. Unambiguous NMR data assignments were achieved by a co mbination of various 2D-NMR techniques. It was clearly demonstrated th at DCRA consists of two different diterpene substrates that are bound together by an intermolecular hydrogen bond and the very good hydropho bic close approach of mutual matching surfaces. In addition, intramole cular hydrogen bonds also contribute to the stabilization of the compl ex.