A CONFORMATIONALLY DEFINED IMINE DERIVATIVE OF PYRIDOXAL - 7,8-DIHYDRO-3-METHYL-2,6-NAPHTHYRIDIN-4-OL

7,8-Dihydro-3-methyl-2,6-naphthyridin-4-ol (9), a cyclic imine derivative of pyridoxal, has been synthesized. The C=N group of this compound lies in a fixed position corresponding to one of the possible conformations of the imine group in pyridoxal phosphate dependent enzymes and opposite to the conformation of hydrogen-bonded imines of pyridoxal previously studied. Although the cyclic imine is catalytically inactive, due to the stability of the six-membered ring which includes the imine group, its electronic absorption spectrum is strikingly similar to those of some pyridoxal phosphate containing enzymes. Derivatives of the cyclic imine have been prepared by oxidation, reduction, and reaction with hydroxylamine. © 1969, American Chemical Society. All rights reserved.