Syntheses of pterocarans, I. Synthesis of both the enantiomers of pterocarpin

✍ Scribed by Mori, Kenji ;Kisida, Hirosi

• Book ID: 102364180
• Publisher: John Wiley and Sons
• Year: 1988
• Tongue: English
• Weight: 357 KB
• Volume: 1988
• Category: Article
• ISSN: 0947-3440
• DOI: 10.1002/jlac.198819880716

✦ Synopsis

Thc first synthesis of (-)-pterocarpin (6) was achieved by rcsolving (*)-2, which in turn was prepared from a known isonavone (1). Unnatural (+ tpterocarpin was also synthesized.

(-)-Pterocarpin (6) was first isolated by Cazeneuve in 1874 as a constituent of red sandalwood, Pterocarpus suntalinus L.". Its structure as depicted in 6 was proposed by the combination of chemical degradation studies2) and 'H-NMR analysis3). Although 6 was known to be optically active as early as in 1887, its absolute configuration remained unknown until the mid-sixties, when It8 et al.' " and Suginome') assigned the stereostructure ( -)-6 for the natural enantiomer of pterocarpin.

Since the discovery of pterocarpin, many compounds with the same 6a,l la-dihydr0-6H-benzofuro[3,2-c]benzopyran ring system were isolated as a group of pterocarpan phytoalexins. We became interested in synthesizing both the enantiomers of pterocarpan phytoalexins so as to know the relationship between stereochemistry and bioactivity. As the first step toward the goal, we decided to establish a general synthetic route to optically active pterocarpans. Herein we describe the first synthesis of pterocarpin enantiomers [( +)-6 and (-)-61 as achieved by the optical resolution of an intermediate (f)-2. R' k2 \ d H -1 OH ( * )-2: R'=H , R'=OH (*)--3;R'=OH, R'=H MeO.