Abstract
Synthesis of DysidinThe synthesis of dysidin ((−)‐1), the enantiomer of a metabolite of the marine sponge Dysidea herbacea, is described. To effect the synthesis, (±)‐5‐isopropyl‐4‐methoxy‐3‐pyrrolin‐2‐one (7) is converted to its lithium salt and reacted with (−)‐(5R,2E)‐3‐methoxy‐5‐trichloromethyl‐2‐hexenoyl chloride ((‐)‐11) to give (−)‐1 and its diastereoisomer (+)‐5‐epidysidin ((+)‐12) epimeric at C(5) of the pyrrolinone ring. The (−)‐acyl chloride (−)‐11 has been synthesized from (+)‐(R)‐3‐(trichloromethyl)butanoic acid ((+)‐8) via the intermediates (+)‐9 and (−)‐10, the pyrrolinone 7 from N‐benzyl‐oxycarbonyl‐L‐valine via the intermediate 5. The enantiomers of acid 8 have been resolved by fractional crystallization of their diastereoisomeric N‐(1‐phenylethyl)amides. The (R)‐chirality of (+)‐8 was determined by comparing the 1H‐NMR spectra of the diastereoisomeric N‐(1‐phenylethyl)amides 16 and 17, made from (+)‐8 by substituting deuterium for chlorine, with the spectra of the N‐(1‐phenylethyl)amides 14 and 15 of known absolute configuration. This correlation shows that literature value (R) for (−)‐8 is in error. Therefore, the structural formulae of (−)‐dysidenin and (+)‐isodysidenin, two other metabolites of D.herbacea, have to be changed to their mirror images as shown in formulae (−)‐3 and (+)‐4, respectively.
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