Synthesis of peptide-oligonucleotide conjugates for chromium coordination

The synthesis of the first peptide-oligonucleotide conjugate designed to coordinate chromium(III) is reported. The overall goal of this work is to synthesize di-deoxynucleotides tethered with chromium-(III)-coordinating appendages to model chromium-DNA-protein cross-links, which are a type of DNA lesion that may be involved in chromium-induced cancers. The conjugate dGp(NHCH₂CH₂S-Ac-Gly-Ser-Gly-OH)G was made by coupling the peptide, ClAc-Gly-Ser-Gly-OH, and dinucleotide, dGp(NHCH₂-CH₂SH)G, through a thioether moiety. The conjugate was characterized by HPLC and mass spectrometry. Previously reported methods for small-scale solid-phase synthesis of peptides and dinucleotide were unsuitable; therefore, gram-scale solution-phase methods were developed. We also report the gram-scale syntheses of two other serine-containing peptides, C1Ac-βAla-Ser-Gly-OH and C1Ac-Ser-Gly-OH, and three histidine-containing peptides, C1Ac-Gly-His-Gly-OH, C1Ac-βAla-His-Gly-OH, and C1Ac-His-Gly-OH. The synthesis and characterization of chromium-containing peptide-oligonucleotide conjugates will ultimately help us to understand chromium-DNA interactions at a molecular level, which is necessary before we can determine how chromium causes cancer.