Monitoring the solid-phase synthesis of depsides and depsipeptides.: A color test for hydroxyl groups linked to a resin.

A color test for the detection of hydroxyl groups bonded to a solid support and useful for the control of solid-phase synthesis of depsides and depsipeptides is described. It is carried out directly on the resin and shows a violet to pink color with primary, secondary and tertiary alcohols, and phenols. 16 mu mol of free OH groups per g of resin can be easily detected with the naked eye using this procedure. The reaction is based on the formation of the tosylate, its displacement with p-nitrobenzylpyridine and conversion of the resin-bound pyridinium salt to a strongly colored internal salt by treatment with base. Amino and carboxyl groups are negative in these conditions. Full loading of Wang and Merrifield resins can be efficiently checked using this test. (C) 1999 Elsevier Science Ltd. All rights reserved.