Combined solid‐phase and solution approach for the synthesis of large peptides or proteins
In the synthesis of large peptides or proteins, highly homogeneous segments are indispensable for a convergent strategy either on a solid‐phase resin or in solution. Employing Boc/Bzl chemistry to prepare fully protected segments with a free α‐carboxyl group from the solid support, base‐labile linkers are profitable for practical peptide synthesis since they require no special equipment. For this purpose, an N‐[9‐(hydroxymethyl)‐2‐fluorenyl]succinamic acid (HMFS) linker was adopted. Consequently, there must be high compatibility between the protecting groups of the segment and the anchoring group which is cleavable by treatment with morpholine or piperidine in DMF. Instead of using the 2‐bromobenzyloxycarbonyl (BrZ) group for the Tyr residue and the formyl (For) group for the Trp residue, both of which are the most susceptible protecting groups under these base‐catalysed conditions, the base‐resistant 3‐pentyl (Pen) and cyclohexyloxycarbonyl (Hoc) groups were introduced to the respective side‐chain functional groups. By applying the present strategy, the authors were able to rapidly synthesize homogeneous protected segments for use in the subsequent segment coupling in solution. In the present paper, the utility of the combined solid‐phase and solution approach is demonstrated by synthesizing muscarinic toxin 1 (MTX1) which binds to the muscarinic acetylcholine receptors. Copyright © 2000 European Peptide Society and John Wiley & Sons, Ltd.
Nin-cyclohexyloxycarbonyl group as a new protecting group for tryptophan
Abstract Several new protecting groups were introduced at the Nin-position of tryptophan, and their reactivities were examined under the conditions used for peptide synthesis by Boc-strategy. Among them, the cyclohexyloxycarbonyl (Hoc) group was found to be the most suitable in terms of stability during elongation of the peptide chain and removability at the final HF reaction without resorting to the use of thiols.
Dimerization of Tryptophan Derivatives in Trifluoroacetic Acid
Side-products are formed when Ac–Trp–OMe, Ac–Gly–Trp–OMe, or Ac–Trp–Trp–OMe is stored in trifluoroacetic acid. Two products from each of Ac–Trp–OMe and Ac–Gly–Trp–OMe and one product from Ac–Trp–Trp–OMe are isolated by the column chromatography on silica gel and confirmed for homogeneity by the highperformance liquid chromatography. As confirmed by 1H-NMR and mass spectral analyses, they have dimerized structures through the α-carbon to α′-carbon binding of two indole rings. One of the two products from each of Ac–Trp–OMe and Ac–Gly–Trp–OMe is the trans-isomer(s) and the other the cis-isomer(s). Only a trans-isomer(s) is obtained from Ac–Trp–Trp–OMe.