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Orthogonally protected a,b-diaminopropionic acids have been synthesised in good yields by the reaction of N-trityl L-serine esters with N-substituted sulfonamides under Mitsunobu reaction conditions (DEAD, PPh3, THF). The best isolated yields were obtained when N-Boc p-toluenesulfonamide was used as the nitrogen nucleophile precursor in the Mitsunobu reaction. Subsequently, the N-trityl group was efficiently replaced with the more stable allyloxycarbonyl (alloc) group.
Kelleher, F. and O'Proinsias, K. Use of the Mitsunobu reaction in the synthesis of orthogonally protected a,b-diaminopropionic acids. Tetrahedron Letters, 48(28):4879-4882. DOI:10.1016/j.tetlet.2007.05.064