PubMed · 4649730
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C M Deber, H Joshua. 1972. Side chain interactions in aromatic dipeptides.. https://doi.org/10.1002/bip.1972.360111209
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By utilizing a pulse-radiolytic technique, we demonstrate for the first time that the rate constant for the reaction of nitric oxide (.NO) with biologically relevant tyrosine and tryptophan radicals (Tyr. and Trp. respectively) in amino acids, peptides and proteins is of the order of (1-2) x 10(9) M-1.s-1. We also show that .NO effectively interferes with electron-transfer processes between tryptophan and tyrosine residues in proteins subjected to pulse radiolysis. The near diffusion-controlled rates of these reactions, coupled with the increasingly recognized role of protein radicals in enzyme catalysis and oxidative damage, suggest that Tyr. and Trp. are likely and important targets for .NO generated in vivo.
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Two stereoselective syntheses of a new pseudodipeptide isostere, the right-hand hydroxyethylene dipeptidomimetic (Xaa psi[CH2CH(OH)]Yaa), are presented. In one method readily available amino acids are used as starting materials for Evans chiral aldol condensation chemistry. The second method relies on the synthesis of an anti-aldol product for the hydroxyethylene isostere via an E-selective ethyl hydrocinnamate enolization, and thus allows for the synthesis of isosteres having side chains other than those available from amino acids. Both methods are illustrated by the chiral synthesis of Boc-Phe psi[CH2CH(OH)]Phe. Two diastereomers, (S,S,R) and (S,R,R), are incorporated into an HIV-1 protease inhibitor template which yields potent inhibitors of HIV-1 protease when the pseudodipeptide isostere is Phe psi[CH(OH)CH2]Phe or Phe psi[CH(OH)CH(OH)]Phe. The resulting Phe psi[CH2CH(OH)]Phe-containing inhibitors possess modest potency.