Abstract: Cys-disulfide bonds contribute to the stabilization of peptide and protein structures. The synthesis of these molecules requires a proper protection of Cys residues, which is crucial to prevent side-reactions and also to achieve the correct Cys connectivity. Here we undertook a mechanistic study of a set of well-known acid-labile Cys protecting groups, as well other new promising groups, in order to better understand the nature of their acid-lability. The stability of the carbocation generated during the acid treatment was found to have a direct impact on the removal of the protective groups from the corresponding protected Cys-containing peptides. Hence a combination of steric and conjugative effects determines the stability of the carbocations generated. Here we propose diphenylmethyl (Dpm) as a promising protecting group on the basis of its intermediate relative carbocation stability. All the optimized geometries and energies presented in this study were determined using a B3LYP/6-31G(d,p) calculation. The results discussed herein may be of broader applicability for the development of new protecting groups.
Keywords: acid lability; benzyl; carbocation stability; Cys protecting groups; diphenylmethyl (Dpm); peptide synthesis
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Ramos-Tomillero, I.; Mendive-Tapia, L.; Góngora-Benítez, M.; Nicolás, E.; Tulla-Puche, J.; Albericio, F. Understanding Acid Lability of Cysteine Protecting Groups. Molecules 2013, 18, 5155-5162.
Ramos-Tomillero I, Mendive-Tapia L, Góngora-Benítez M, Nicolás E, Tulla-Puche J, Albericio F. Understanding Acid Lability of Cysteine Protecting Groups. Molecules. 2013; 18(5):5155-5162.
Ramos-Tomillero, Iván; Mendive-Tapia, Lorena; Góngora-Benítez, Miriam; Nicolás, Ernesto; Tulla-Puche, Judit; Albericio, Fernando. 2013. "Understanding Acid Lability of Cysteine Protecting Groups." Molecules 18, no. 5: 5155-5162.