| Abstract
| - Stereochemical studies of a cruciferous oxindole phytoalexin, (S)-(−)-spirobrassinin [(−)-4], andits oxazoline analogue, spirooxazoline (11), were carried out. Racemic spirobrassinin [(±)-4] wassynthesized by SOCl2- or MsCl-mediated cyclization of dioxibrassinin [(±)-8]. Treatment of(3-hydroxyoxindol-3-yl)methylammonium chloride [(±)-9] with CSCl2 and subsequent methylationof the obtained spirooxazolidinethione (±)-10 afforded spirooxazoline [(±)-11]. Enantioresolutionof (±)-4 and (±)-11 was achieved by derivatization with (S)-(−)-1-phenylethyl isocyanate (12),chromatographic separation of diastereomeric amides 13, 14 or 15, 16, and their cleavage withCH3ONa. Absolute configuration of the stereogenic center in natural (S)-(−)-4 was derived fromthe exciton, calculated via CD methods, and unequivocally confirmed by X-ray crystallographicanalyses of 1-[1‘S,4‘R-(−)-camphanoyl] derivatives [(−)-19 and (−)-20] of (+)- and (−)-4. Novelenantiomeric enrichment phenomena of 4 and 11 were discovered during their chromatographicseparations under achiral HPLC conditions. Screening of antifungal activity against the fungusBipolaris leersiae revealed no significant dependence of this activity on absolute configuration.
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