Total synthesis and stereochemical assignment of cis-uvariamicin I and cis-reticulatacin.

Diastereoisomeric mixtures of cis-uvariamicin I (15R,16R,19S,20S,36S and 15S,16S,19R,20R,36S) and cis-reticulatacin (17R,18R,21S,22S,36S and 17S,18S,21R,22R,36S) were synthesized to determine the stereochemistry of the natural products isolated from Annona muricata. It was not possible to resolve a mixture of the four synthetic isomers using chiral HPLC, but the mixed isomers could be distinguished using chiral HPLC EIMS with extracted fragment ion analysis. Comparison of synthetic standards with the natural isolate revealed that cis-uvariamicin I and cis-reticulatacin are present in nature as mixtures of threo-cis-threo diastereoisomers. It is suggested that the nomenclature for the natural products is amended as follows: (15R,16R,19S,20S,36S)-cis-uvariamicin I (cis-uvariamicin IA); (15S,16S,19R,20R,36S)-cis-uvariamicin I (cis-uvariamicin IB); (17R,18R,21S,22S,36S)-cis-reticulatacin (cis-reticulatacin A); (17S,18S,21R,22R,36S)-cis-reticulatacin (cis-reticulatacin B).