Chemistry of Chiral Vitamin B6 Analogs. IV. Syntheses of Chiral Pyridoxal and Pyridoxamine Analogs Having a Branched “Ansa Chain” between 2′- and 5′-Positions

Racemic 15-formyl-14-hydroxy-5,5-dimethyl-2,8-dithia[9](2,5)pyridinophane (4), an analog of pyridoxal having a branched “ansa chain” between 2′- and 5′-positions, was synthesized from 2,5-bis(chloromethyl)-3-hydroxy-O,O′-isopropylidene-4-pyridinemethanol. Optical resolution of 4 was achieved via the formation of Schiff base with 3-amino-3-deoxy-1,2:5,6-di-O-isopropylidene-d-glucofranose, giving the levorotary enantiomer of 4 (4a). Racemic 15-aminomethyl-14-hydroxy-5,5-dimethyl-2,8-dithia[9](2,5)pyridinophane (5), the same type of pyridoxamine analog as 4, and its levorotary enantiomer were synthesized from the corresponding 4 and 4a. Both levorotary and dextrorotary enantiomers of 5 were also obtained by the optical resolution of the racemate via the formation of chiral dibenzoyltartaric acid salts of 5.