Synthesis of disubstituted 1,3,4,9-tetrahydropyrano-[3,4-b]indole-1-acetic acids derivatives

1,3,4,9-tetrahydropyrano[3,4-b]indole-1-acetic acid derivatives are of interest for pharmaceutical research as a core structure for synthesis of biological active substance Etodolac (selective Cyclooxygenase-2 inhibitor, which belongs to the Nonsteroidal Anti-inflammatory Drug, NSAID, that shows a clinically effective analgesic and anti-inflammatory activity). Here the way of synthesis of two 1,3,4,9-tetrahydropyrano[3,4-b]indole1-acetic acid derivatives, impurities of Etodolac generated during drug production process, is presented. The title compounds were prepared in eight steps procedure which differs from previously reported with respect to the way of constructing 1,3,4,9tetrahydropyranring in molecule. Moreover, reaction conditions have been optimised and more efficient purification methods were introduced.