Yongseok Choi, Clifford George, Peter Strazewski, and Victor E. Marquez* Organic Letters 2002, 4, 589-592. Synthesis of a Conformationally Locked Version of Puromycin Amino Nucleoside   A conformationally locked carbocyclic version of puromycin amino nucleoside was synthesized via Mitsunobu coupling of a 3-azido-substituted carbocyclic moiety with 6-chloropurine without interference from the azido group reacting with triphenylphosphine. The requisite 3-azido-substituted carbocyclic pseudosugar was prepared by a double inversion of configuration at C3' (nucleoside numbering) involving a nucleophilic displacement with azide.