From carnitinamide to 5-aminomethyl-2-oxazolidinones

Carnitinamide chloride, an immediate synthetic precursor of carnitine, was chlorinated at the amide nitrogen. The resultant carnitinechloramide chloride, when treated with a base, revealed that the first-formed isolable and characterisable carnitinechloramide inner salt undergoes solid state conversion into 5-trimethylammoniomethyl-2-oxazolidinone chloride via Hoffmann rearrangement and intramolecular cyclization of the β-hydroxyisocyanate. The trimethylaminomethyl substituent at C-5 of the 2-oxazolidinone was converted into a dimethylaminomethyl group by microwave-assisted demethylation in DMF and then into a methylaminomethyl group by decomposition of the α-chloroethyl carbamate obtained by treatment with α-chloroethyl chloroformate. This sequence of reactions was then applied to both (S)- and (R)-carnitinamide chloride without any racemization to yield both enantiomers of 5-aminomethyl-2-oxazolidinones that are mono-, di- and tri-methylated at the exocyclic nitrogen.