 Retinyl ester

A retinyl ester is an ester formed at the alcohol group of retinol. The retinyl portion is attached through oxygen to an acyl group; different attached groups produce different members of the class. The name therefore does not identify one unique molecular formula or molar mass.^[ref]

Write a retinol alcohol schematically as $\mathrm{Ret}-\mathrm{OH}$, where Ret represents its carbon framework. The corresponding ester has the arrangement $\mathrm{Ret}-\mathrm{O}-\mathrm{C}(=\mathrm{O})-\mathrm{R}$. Varying $R$ changes the attached acyl group without requiring a change in the retinyl framework. This is a structural comparison, not a claim that a free carboxylic acid supplies every biological esterification reaction.

For example, lecithin retinol acyltransferase uses phosphatidylcholine as an acyl donor. Its products include retinyl esters that can be stored or used in subsequent retinoid pathways.^[ref] An assay of total ester therefore needs an additional identity measurement if the question concerns a particular ester, geometric isomer or downstream substrate.