title: Solid-phase peptide synthesis by ion-paired alpha-chymotrypsin in nonaqueous media.
abstract: Solid-phase synthesis of dipeptides in low-water media was achieved using AOT ion-paired alpha-chymotrypsin solubilized in organic solvents. Multiple solvents and systematic variation of water activity, a(w), were used to examine the rate of coupling between N-alpha-benzyloxycarbonyl-L-phenylalanine methyl ester (Z-Phe-OMe) and leucine as a function of the reaction medium for both solid-phase and solution-phase reactions. In solution, the observed maximum reaction rate in a given solvent generally correlated with measures of hydrophobicity such as the log of the 1-octanol/water partitioning coefficient (log P) and the Hildebrand solubility parameter. The maximum rate for solution-phase synthesis (13 mmol/h g-enzyme) was obtained in a 90/10 (v/v) isooctane/tetrahydrofuran solvent mixture at an a(w) of 0.30. For the synthesis of dipeptides from solid-phase leucine residues, the highest synthetic rates (0.14-1.3 mmol/h g-enzyme) were confined to solvent environments that fell inside abruptly defined regions of solvent parameter space (e.g., log P > 2.3 and normalized electron acceptance index <0.13). The maximum rate for solid-phase synthesis was obtained in a 90/10 (v/v) isooctane/tetrahydrofuran solvent mixture at an a(w) of 0.14. In 90/10 and 70/30 (v/v) isooctane/tetrahydrofuran environments with a(w) set to 0.14, seven different N-protected dipeptides were synthesized on commercially available Tentagel support with yields of 74-98% in 24 h.
authors.affiliation: Department of Chemical Engineering, University of California, Berkeley, California 94720-1462, USA.
authors.forename: David H
authors.initials: DH
authors.lastname: Altreuter
authors.forename: Jonathan S
authors.initials: JS
authors.lastname: Dordick
authors.forename: Douglas S
authors.initials: DS
authors.lastname: Clark
mesh_terms: D002384:Catalysis; D002918:Chymotrypsin / Q000737:chemistry*; D004151:Dipeptides / Q000138:chemical synthesis*; D006923:Hymecromone / Q000031:analogs & derivatives* / Q000737:chemistry*; D007930:Leucine / Q000737:chemistry*; D010455:Peptides / Q000138:chemical synthesis; D012995:Solubility; D012997:Solvents / Q000737:chemistry*; D014867:Water / Q000737:chemistry
chemical_list: D004151:Dipeptides; D010455:Peptides; D012997:Solvents; D014867:Water; D006923:Hymecromone; C047960:benzyloxycarbonylphenylalanine 4-methylcoumaryl-7-ester; D002918:Chymotrypsin; C117608:alpha-chymotrypsin; D007930:Leucine