Abstract
Readily available natural α-amino acids are one of nature’s most attractive and versatile building blocks in synthesis of natural products and biomolecules. Peptides and N-heterocycles exhibit various biological and pharmaceutical functions. Conjugation of amino acids or peptides with N-heterocycles provides boundless potentiality for screening and discovery of diverse biologically active molecules. However, it is a great challenge to install amino acids or peptides on N-heterocycles through formation of carbon-carbon bonds under mild conditions. In this article, eighteen N-protected α-amino acids and three peptides were well assembled on phenanthridine derivatives via couplings of N-protected α-amino acid and peptide active esters with substituted 2-isocyanobiphenyls at room temperature under visible-light assistance. Furthermore, N-Boc-proline residue was successfully conjugated with oxindole derivatives using similar procedures. The simple protocol, mild reaction conditions, fast reaction, and high efficiency of this method make it an important strategy for synthesis of diverse molecules containing amino acid and peptide fragments.
Highlights
After getting the optimized conditions under visible-light assistance, we investigated the substrate scope of this reaction by testing decarboxylative couplings of various N-protected amino acid active esters (1) with substituted 2-isocyanobiphenyls (2)
We explored synthesis of oxindole derivatives under visible-light photoredox catalysis by using N-protected amino acid active esters
The photoredox-generated α -amino or peptide radicals were trapped with substituted 2-isocyanobiphenyls or N-alkyl-N-phenylalkacrylamides at room temperature, and the phenanthridine and oxindole derivatives with biological and pharmaceutical activity were prepared in good yields
Summary
Effect of solvents was explored, and DMF provided the best result (compare entries 3, 11–13). The reaction in aqueous media (DMF/H2O = 9:1) was attempted, and a 92% yield was provided (entry 14). After getting the optimized conditions under visible-light assistance, we investigated the substrate scope of this reaction by testing decarboxylative couplings of various N-protected amino acid active esters (1) with substituted 2-isocyanobiphenyls (2).
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