Three Protected Tetrapeptides

The structures of three protected tetrapeptides, containing the Boc-Gly-Gly-Phe-X-OMe chain, tert-butoxycarbonyl-glycy-glycl-phenylalanine-leucine methyl ester dihydrate, Boc-Gly-Gly-L-Phe-D-Leu-OMe, C₂₅H₃₈N₄O₇·2H₂O, tert-butoxycarbonyl-glycy-glycl-phenylalanine-methionine methyl ester dihydrate, Boc-Gly Gly-L-Phe-D-Met-OMe, C₂₄H₃₆N₄O₇S.2H₂O and tert-butoxycarbonyl-glycy-glycl-phenylalanine-norleucine methyl ester dihydrate, Boc-Gly-Gly-D-Phe-L-Nle-OMe, C₂₅H₃₈N₄O₇.2H₂O, are described. The three molecules have the same conformation of the Boc-Gly Gly Phe-X-OMe tetra­peptide chain and display the same packing, consisting of couples of molecules linked head-to-tail by two hydrogen (N-H...O) bonds; other hydrogen bonds, also involving two water molecules of crystallization, link these couples together, and give rise to a planar structure.

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