Stemmosides C and D, two novel unusual pregnane glycosides from Solenostemma argel: structural elucidation and configurational study by a combined NMR-quantum mechanical strategy

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• 作者：Plaza ; Alberto ; Piacente ; Sonia ; Perrone ; Angela ; Hamed ; Arafa ; Pizza ; Cosimo ; Bifulco ; Giuseppe
• 关键词：Natural products ; Solenostemma argel ; Steroids ; NMR ; DFT calculations ; GIAO
• 刊名：Tetrahedron
• 出版年：2004
• 期刊代码：107_00404020
• 类别：ch
• 出版时间：December 20, 2004
• 卷：60
• 期：52
• 页码：12205-12213
• 文件大小：234 K

摘要

Stemmosides C and D, two novel pregnane glycosides characterized by an unusual C-17α side chain were isolated from the pericarps of Solenostemma argel. In addition, stemmoside D displays an uncommon 14β proton configuration, apparently being the first pregnane isolated from plants known to have a 15 keto, cis CD ring junction. Their structures have been established by ESIMS and NMR experiments. The relative configuration of the molecules was determined using a strategy based on the simulation of ¹H, ¹³C, and J coupling NMR parameters. DFT calculations of ¹H and ¹³C chemical shifts, and of the ¹H homonuclear spin–spin coupling constants were performed with the mPW1PW91 functional using the 6-31G(d,p) basis set on the fully optimized geometries of all the possible stereoisomers.