The chemistry of heterocyclic compounds is an important and vast branch of organic chemistry. Synthetic heterocyclic chemistry has influenced almost every walk of human life and the synthesized compounds make up a significant percentage in various field as medicine, agriculture, industries and are widely distributed in nature as vitamins, hormones, nucleic acids, alkaloids and antibiotics. In this vein different compounds possessing benzo[a]phenothiazine, pyrido[2,3-d]pyrimidine and 10H-pyrido[3,2-b][1,4]benzothiazine ring system and their nucleosides have been synthesized and studied spectrophotometrically.