The Role of Total Synthesis in Structure …
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Chart 4 (S)-Phoracantholide I ((S)-124) and possible structures of the second constituent of the
gland extracts from Mantidactylus femoralis
was proposed based on its mass spectrum. Out of all constitutional isomers plausible, biosynthesis pathways exist for the four isomers 125–128, which were then
synthesized as mixtures of stereoisomers using RCM and hydrogenation (Chart 4).
Comparison with the GC-MS trace of the gland extract excluded structures 125,
127 and 128, and pointed to 4-methyl-9-decanolide (126) as the correct constitution
of the second major gland extract component. In the next step all four stereoisomers of
126 were synthesized selectively and submitted to GC-analysis on a chiral stationary
phase. This revealed that the structure of the novel natural product, for which the
name mantidactolide A was proposed, is (4R,9S)-126 (Scheme 25).
Scheme 25 Stereoselective synthesis of mantidactolide A ((4R,9S)-126) as a reference sample
43
Chart 4 (S)-Phoracantholide I ((S)-124) and possible structures of the second constituent of the
gland extracts from Mantidactylus femoralis
was proposed based on its mass spectrum. Out of all constitutional isomers plausible, biosynthesis pathways exist for the four isomers 125–128, which were then
synthesized as mixtures of stereoisomers using RCM and hydrogenation (Chart 4).
Comparison with the GC-MS trace of the gland extract excluded structures 125,
127 and 128, and pointed to 4-methyl-9-decanolide (126) as the correct constitution
of the second major gland extract component. In the next step all four stereoisomers of
126 were synthesized selectively and submitted to GC-analysis on a chiral stationary
phase. This revealed that the structure of the novel natural product, for which the
name mantidactolide A was proposed, is (4R,9S)-126 (Scheme 25).
Scheme 25 Stereoselective synthesis of mantidactolide A ((4R,9S)-126) as a reference sample