Crystal Structure of Garciniaphenone and Evidences on the Relationship between Keto–Enol Tautomerism and Configuration

✍ Scribed by Felipe T. Martins; I. Camps; Antônio C. Doriguetto; Marcelo H. dos Santos; Javier Ellena; Luiz C. A. Barbosa

• Publisher: John Wiley and Sons
• Year: 2008
• Tongue: German
• Weight: 248 KB
• Volume: 91
• Category: Article
• ISSN: 0018-019X
• DOI: 10.1002/hlca.200890143

✦ Synopsis

Abstract

Garciniaphenone (=rel‐(1__R__,5__R__,7__R__)‐3‐benzoyl‐4‐hydroxy‐8,8‐dimethyl‐1,7‐bis(3‐methylbut‐2‐en‐1‐yl)bicyclo[3.3.1]non‐3‐ene‐2,9‐dione; 1), a novel natural product, was isolated from a hexane extract of Garcinia brasiliensis fruits. The crystal structure of 1 as well as the selected geometrical and configurational features were compared with those of known related polyprenylated benzophenones. Garciniaphenone is the first representative of polyprenylated benzophenones without a prenyl substituent at C(5). Notably, the absence of a 5‐prenyl substituent has an impact on the molecular geometry. The tautomeric form of 1 in the solid state was readily established by a residual‐electronic‐density map generated by means of a difference Fourier analysis, and there is an entirely delocalized six‐membered chelate ring encompassing the keto–enol moiety. The configuration at C(7) was used to rationalize the nature of the keto–enol tautomeric form within 1. The intermolecular array in the network is maintained by nonclassical intermolecular H‐bonds.