16-02

B. Zwanenburg, H. Regeling, C.W. van Tilburg-Joukema, B. van Oss, P. Molenveld, R. de Gelder, P. Tinnemans,

Securing important strigolactone key structures: orobanchol and 5-deoxystrigol,

Eur. J. Org. Chem. (2016) 21-63-2169

Abstract

Strigolactones (SLs) constitute an important new class of plant hormones. Their isolation from natural resources, such as root exudates, is laborious and difficult. Therefore, synthetic SLs are needed to discover their (biological) properties. Such syntheses involve many steps. When repeating a published procedure for the synthesis of orobanchol, we noticed that the structure of the synthesized material was ambiguous. This structure was secured by means of X-ray analysis. An essential step in the synthesis, namely an allylic oxidation of the ABC scaffold, was significantly improved by using Pd/C and tert-butyl hydroperoxide (Corey's method). The second issue deals with the structure of the four stereoisomers of 5-deoxystrigol. The stereochemistry of these compounds was based on the use of Welzel's empirical rules for CD spectra. By means of X-ray analysis the stereochemistry of one of the stereoisomers was established unambiguously, thereby securing the configuration of all four isomers.