Aryldithioethyloxycarbonyl(Ardec):A New Family of Amine Protecting Groups Removable under Mild Reducing Conditions and Their Applications to Peptide Synthesis

摘要

The development of phenyl-dithioethyloxycarbonyl(Phdec)and 2-pyridyldithioethyloxycarbonyl(Pydec)protecting groups,which are thiol-labile urethanes,is described.These new disulfide-based protecting groups were introduced onto the e-amino group of L-lysine;the resulting amino acid derivatives were easily converted into N~(alpha)-Fmoc building blocks suitable for both solid-and solution-phase pep-tide synthesis.Model dipeptide-(Ardec)s were prepared by using classical peptide couplings followed by standard deprotection protocols.They were used to optimize the conditions for complete thiolytic removal of the Ardec groups both in aqueous and organic media.Phdec and Pydec were found to be cleaved within 15 to 30 min under mild reducing conditions:i)by treatment with dithiothreitol or(3-mercaptoethanol in Tris centre dot HCl buffer (pH 8.5-9.0)for deprotection in water and ii)by treatment with beta-mercapto-ethanol and 1,8-diazobicyclo-[5.4.0]undec-7-ene(DBU)in N-methyl-pyrrolidinone for deprotection in an organic medium.Successful solid-phase synthesis of hexapeptides Ac-Lys-Asp-Glu-Val-Asp-Lys(Ardec)-NH_2 has clearly demonstrated the full orthogonality of these new amino protecting groups with Fmoc and Boc protections.The utility of the Ardec orthogonal de-protection strategy for site-specific chemical modification of peptides bearing several amino groups was illustrated firstly by the preparation of a fluo-rogenic substrate for caspase-3 protease containing the cyanine dyes Cy3.0 and Cy5.0 as FRET donor/acceptor pair,and by solid-phase synthesis of an hexapeptide bearing a single biotin reporter group.