Strophiofimbrins A and B: Two Rearranged Norditerpenoids with Novel Tricyclic Carbon Skeletons from Strophioblachia fimbricalyx

Abstract

Two rearranged norditerpenoids with novel tricyclic carbon skeletons, strophiofimbrin A (1) and strophiofimbrin B (2), were isolated from Strophioblachia fimbricalyx. Their structures were established by 1D/2D NMR spectroscopy, HRESIMS, quantum chemistry calculations, and X-ray diffraction analyses. 1 and 2 represented the first examples of diterpenoids with unprecedented 5/6/7-fused ring systems. In the proposed biosynthetic pathway, they were suspected to derive from cleistanthane norditerpenoids via ring opening, expansion, cyclization, and rearrangement based on the existence of phenanthrenone and cleistanthane diterpenoids from Strophioblachia and Trigonostemon, two closely related genera of the Euphorbiaceae family. Furthermore, compounds 1 and 2 exhibited significant proliferation inhibition and obvious neuroprotective effects.

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“…The structure of the rearranged norditerpenoid strophiofimbrin A 15 , from Strophioblachia fimbricalyx , was confirmed by X-ray analysis and a biosynthetic pathway for its formation from a podocarpane derivative has been proposed. 13 The structure of saldigitin A 16 , from Salvia digitaloides , was also confirmed by X-ray analysis. 14 It is suggested that saldigitin A 16 is formed from an abietane diterpenoid involving pinacol rearrangement, ring cleavage and Michael addition steps.…”