X-Ray Crystal Structure Analysis of Oxindole Alkaloids

✍ Scribed by Gerhard Laus; Klaus Wurst

• Publisher: John Wiley and Sons
• Year: 2003
• Tongue: German
• Weight: 124 KB
• Volume: 86
• Category: Article
• ISSN: 0018-019X
• DOI: 10.1002/hlca.200390009

✦ Synopsis

Abstract

The single‐crystal X‐ray structures of speciophylline, mitraphylline, and rhynchophylline, oxindole alkaloids from the Peruvian climbing vine Uncaria tomentosa (Rubiaceae), were determined. The three compounds show N⋅⋅⋅HN hydrogen bonding, which has not been observed in the crystal structures of the related alkaloids pteropodine and isopteropodine. In the tetracyclic alkaloid rhynchophylline, the side chain is rotated out of the ring plane into a position perpendicular to it. This is in contrast to the situation of the pentacyclic analogue mitraphylline, which possesses a conformationally rigid tricyclic core. This conformational difference possibly causes the competitive antagonism of these two types of alkaloids.