The nine-carbon fatty acid 9-hydroxy-nonanoic acid (9-HN) is derived as a separate compound and later esterified to monic acid to form pseudomonic acid. 13 C labeled acetate feeding has shown that C1-C6 are constructed with acetate in the canonical fashion of fatty acid synthesis . C7' shows only C1 labeling of acetate, while C8' and C9' show a reversed pattern of 13C labeled acetate.  It is speculated that C7-C9 arises from a 3-hydroxypropionate starter unit, which is extended three times with malonyl-CoA and fully reduced to yield 9-HN. It has also been suggested that 9-HN is initiated by 3-hydroxy-3-methylglutaric acid (HMG). This latter theory was not supported by feeding of [3- 14 C] or [3,6- 13 C 2 ]-HMG.