Incorporation of CH313C18O2Na and CD3CH213CO2Na into the indolizidine alkaloid cyclizidine 1, produced by Streptomyces species NCIB 11649, shows that the oxygen attached to C-2 is derived intact from acetate and that the cyclopropyl ring is derived from a single intact propionate unit. However, the level and stereochemistry of the incorporation of deuteriated sodium propionate indicates that it undergoes unexpected modification during ...