A modular synthesis of alkynyl-phosphocholine headgroups for labeling sphingomyelin and phosphatidylcholine

A general route to phospho- and sphingolipids that incorporate an alkyne in the phosphocholine headgroup is described. The strategy preserves the ammonium functionality of the phosphocholine and can be easily modified to introduce desired functional groups at the N-acyl chain. The targets accessible with this strategy provide a bioorthogonal handle for postsynthetic introduction of fluorophores or other labeling agents with aqueous phase chemistry. We report the synthesis of sphingomyelin derivatives that incorporate a fluorophore and an alkyne. The modified sphingolipids retain activity as substrates for sphingomyelinase, making these compounds viable probes of enzymatic activity. Importantly, the strategy allows modification of the lipid across the phosphodiester, making the alkyne a potential probe of sphingomyelinase activity.