Synthesis of C-11 linked active ester derivatives of vitamin D3 and their conjugations to 42-residue helix loop helix peptides

Derivatives of vitamin D-3 carrying an 8-carbon linker at C-11 terminating in an active ester were synthesized from commercial vitamin D3 using a disassembly reassembly strategy. Vitamin D3 was cleaved at the C6-C7 double bond and the 'upper' fragment was converted, via a series of reactions, to derivatives substituted at C-11 with an 8-carbon linker terminating in an ethyl ester. Reassembly with modified 'lower' fragments using Horner-Wittig olefination followed by linker ester hydrolysis and reesterification with p-nitrophenol gave C-11 substituted p-nitrophenyl esters. These vitamin D derivatives were conjugated to 42-amino acid helix loop helix peptides by reaction of their p-nitrophenyl esters with lysyl side-chain amino groups on the peptides. The vitamin D peptide conjugates, being potential specific binder candidates for vitamin D-binding protein, were characterized by mass spectroscopy and CD measurements. (C) 2010 Elsevier Ltd. All rights reserved.