Solubilization of Peptides in Non-polar Organic Solvents by the Addition of Inorganic Salts: Facts and Implications

The solubility of open-chain peptide derivatives (12 examples) in non-polar, ether-type organic solvents may be greatly increased by addition of salts (LiCl, LiBr, LiI, LiBF₄, LiClO₄, NaI, MgBr₂ CaBr₂, ZnCl₂) or of titanates (Ti(OEt)₄, Ti(OCHMe₂)₄). Examples are reported (Tables 2–6) in which this solubilizing effect leads to peptide concentrations more than one-hundred-fold those in the absence of salt (cf, Boc? Ala? Gly? Gly? Gly? OH in THF from 2g·1^?1 to ≥ 300 g·1^?1 with 6 equiv. of LiCl), ¹H-NMR Spectra of one of these solutions are reported (Fig. 1). There are no indications for epimerizations of stereogenic centres on the peptide backbone. Possible applications of these solutions in peptide chemistry are discussed.