Discovery Through Total Synthesis—Epimerization at C7 in the CP Compounds: Is (7S)-CP-263,114 a Fermentation Product?

Sometimes a surprise can occur in a total synthesis. The preparative investigation of the title compound CP-263,114 and of CP-225,917 (1)-both natural products that were first isolated in 1997 by Pfizer-has shown that CP compounds of the 7R series can be converted into the 7S series (for example, 2); (7S)-CP-263,114 is itself apparently a fermentation product.