Propionyl-CoA is produced as an intermediate of odd chain fatty acid oxidation. Propionyl-CoA is produced by thiolytic cleavage of the five-carbon homolog of acetoacetyl-CoA (see here).

Propionyl-CoA can be converted to D-Methylmalonyl-CoA by the enzyme propionyl-CoA carboxylase via addition of a carboxyl group (from bicarbonate) in the presence of ATP (Figure 18.19).