Construction of a chiral quaternary carbon center by a radical cyclization/ring-enlargement reaction: synthesis of 4α-azidoethyl carbocyclic ribose, a key unit for the synthesis of cyclic ADP-ribose derivatives of biological importance

Abstract

As a stable analog of the second messenger cyclic ADP-ribose (cADPR), we designed 4″-azidoethyl-cyclic ADP-carbocylic-ribose (N3-cADPcR). For the synthesis of N3-cADPcR, 1β-amino-2,3-O-isoproplylidene-4α-azidoethyl carbocyclic-ribose (4) having a chiral quaternary stereogenic center is required as the key unit. We successfully synthesized the desired unit 4 via construction of the quaternary stereogenic center by a radical cyclization/ring-enlargement reaction with a silicon-tethered substrate as the key step.