p-Nitrobenzhydryl oxime polystyrene

Labile to basic and nucleophilic conditions. Used for convenient preparation of protected fragments, cyclic peptides, and alternative C-terminal groups. Oxime resin is a synthesis resin compatible with Boc chemistry. Substrates can be cleaved from this resin under basic conditions, which leave the side chain and N-terminal protecting groups in place, making this resin very useful for preparing protected fragments that can be used in the segment condensation synthesis of larger substrates. This resin is also useful for preparing structural analogues which differ only at the C-terminus. By using different alkyl amines to displace the substrate from the resin, a series of N-alkylamides of the same substrate can be prepared. Likewise, using DBU and different alcohols a variety of esters can be prepared. Using acetate salts of amino acid esters produces a series of peptide analogues that differ only in the C-terminal amino acid. Although this resin is compatible with Boc chemistry, the oxime ester linkage is susceptible to TFA. Therefore, the Boc group is removed with 25% TFA in DCM during synthesis and end-capping is performed after each coupling to block any active sites on the resin that may have been exposed. References Pichette, A., et al.; Tetrahedron Lett. 1997; 38: 1279. Lee, B.H. et al.; Tetrahedron Lett. 1997; 38: 757. Mohan, R.; Chou, Y.-L.; Morrissey, M.M.; Tetrahedron Lett. 1996; 37: 3963. Scialdone, M.A.; Tetrahedron Lett. 1996; 37: 8141. Carpino, L.A.; El-Faham, A.; J. Am. Chem. Soc. 1995; 117: 5401. Nishino, N., et al.; Tetrahedron Lett. 1992; 33: 1479. Sasaki, T., et al.; J. Org. Chem. 1991; 56: 3159. DeGrado, W.F.; Kaiser, E.T.; J. Org. Chem. 1982; 47: 3258. DeGrado, W.F.; Kaiser, E.T.; J. Org. Chem. 1980; 45: 1295.