Aminocatalysis-Mediated on-Resin Ugi Reactions: Application
in the Solid-Phase Synthesis of <i>N</i>‑Substituted
and Tetrazolo Lipopeptides and Peptidosteroids
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Abstract
A new solid-phase
protocol for the synthesis of <i>N</i>-substituted and tetrazolo
peptides is described. The strategy relies
on the combination of aminocatalysis-mediated on-resin Ugi reactions
and peptide couplings for the <i>N</i>-alkylation of peptides
at selected sites, including the <i>N</i>-terminal double
lipidation, the simultaneous lipidation/biotinylation, and the steroid/lipid
conjugation via tetrazole ring formation. The solid-phase Ugi four-component
reactions were enabled by on-resin transimination steps prior to addition
of the acid and isocyanide components. The strategy proved to be suitable
for the feasible incorporation of complex <i>N</i>-substituents
at both termini and at internal positions, which is not easily achievable
by other solid-phase methods