C-3 Epimerization of 6-Deoxocastasterone in Phaseolus vulgaris

Abstract

Brassinosteroids (BRs) are steroidal plant hormones, which exert a variety of regulatory effects relevant to plant growth and development. 1-5 Thus far, over 40 different BRs have been identified throughout the entirety of the plant kingdom. 6,7 Among the plants so far tested for their BR contents, the immature seeds of Phaseolus vulgaris represent one of the richest. 11 BRs have been fully characterized from this source, whereas the presence of more than 60 additional unknown BRs has been demonstrated via capillary GC-MS analyses. Our interest in the structure and metabolism of BRs compelled us to conduct a series of investigations into the unknown BRs contained in the seeds of P. vulgaris, by scaling up and employing a sizeable quantity of the plant materials. As a result, we have identified a new BR, designated 3-epi-6-deoxoCS. Herein, we report the isolation, characterization, and biogenesis of this BR in Phaseolus seeds.The ethyl acetate soluble fraction acquired from the Phaseolus seeds (136 Kg) was purified with SiO 2 , repeated Sephadex LH-20, and charcoal chromatography, 8 under the guidance of a rice lamina inclination bioassay. 9 Further purification was then conducted via reversed-phase HPLC (Senshupak Develosil, 20 × 250 mm), 8 and the resulting HPLC fractions were derivatized to bismethaneboronate (BMB), then analyzed using a capillary GC-MS: HP 5973 mass spectrometer (EI, 70 eV, Hewlett Packard) connected to a 6890 gas chromatograph equipped with a fused silica capillary column (HP-5, DB-5, 0.25 × 30 mm). 10