Synthesis of [13C₃]-B6 Vitamers Labelled at Three Consecutive Positions Starting from [13C₃]-Propionic Acid.

[13C₃]-labelled vitamers (PN, PL and PM) of the B6 group were prepared starting from [13C₃]-propionic acid. [13C₃]-PN was synthesized in ten linear steps with an overall yield of 17%. Hereby, higher alkyl homologues of involved esters showed a positive impact on the reaction outcome of the intermediates in the chosen synthetic route. Oxidation of [13C₃]-PN to [13C₃]-PL was undertaken using potassium permanganate and methylamine followed by acid hydrolysis of the imine derivative. [13C₃]-PM could be prepared from the oxime derivative of [13C₃]-PN by hydrogenation with palladium.