13acetate

13-acetate, written as 13-acetate or 13-acetyl ester, is a chemical designation used for ester derivatives in which an acetyl group (CH3-CO–) is esterified to a molecule at its 13-position. The term is most commonly encountered in steroid chemistry, where the cyclopentanoperhydrophenanthrene nucleus is numbered in a standard way; a 13-acetate would refer to the acetate ester formed from a 13-hydroxyl group. In other polycyclic systems, 13 can denote a position on the ring system or a side chain; the exact structure depends on the parent compound.

Preparation is by acetylation of the corresponding 13-hydroxyl compound, using acetic anhydride or acetyl chloride in the presence of base (for example pyridine or DMAP) or under Friedel–Crafts–type conditions if the 13-hydroxyl is activated. The resulting ester is typically more lipophilic than the parent alcohol and often serves as a prodrug or intermediate in synthesis; it can be hydrolyzed back to the 13-hydroxyl compound by esterases or under acidic or basic hydrolysis.

13-acetates are used in medicinal chemistry to adjust pharmacokinetic properties or to serve as protective groups during multi-step syntheses. They are one class of acetate esters among many position-specific acetylated derivatives. Analytical characterization commonly employs NMR and mass spectrometry, with the acetyl methyl appearing around 2.0–2.1 ppm in 1H NMR and the carbonyl around 170–175 ppm in 13C NMR.

See also: acetate ester, acetyl group, steroid chemistry.