In an attempt to elucidate the role of pyridoxal 5′-phosphate in the structure and function of glycogen phosphorylase, a series of analogs of the cofactor, modified in various positions around the pyridine ring, have been synthesized. This paper reports the unambiguous synthesis of 3-O-methylpyridoxal, 3-O-methylpyridoxal oxime, 3-O-methylpyridoxamine, 3-O-methylpyridoxamine 5′-phosphate, 3-Omethylpyridoxal 5′-phosphate, N-methylpyridoxal oxime, N-methylpyridoxamine, N-methylpyridoxamine 5′-phosphate, N-methylpyridoxal 5′-phosphate, isopyridoxamine 4′-phosphate, and isopyridoxal 4′-phosphate. The chemical properties of these compounds including their spectral characteristics and pKa values are described. The following publication reports the enzymatic properties of these and other pyridoxal phosphate analogs in the reconstitution of muscle glycogen apophosphorylase. © 1969, American Chemical Society. All rights reserved.