1. Tert.-butylcarbamoylquinine as chiral ion-pair agent in non-aqueous enantioselective capillary electrophoresis applying the partial filling technique
M Lämmerhofer, E Zarbl, W Lindner J Chromatogr A. 2000 Sep 15;892(1-2):509-21. doi: 10.1016/s0021-9673(00)00172-2.
The potential of tert.-butylcarbamoylquinine as chiral selector (SO) added to a non-aqueous background electrolyte for the capillary electrophoretic separation of the enantiomers of N-derivatized amino acids (selectands, SAs) is evaluated. Separation is based on different ion-pair formation equilibrium constants of (R) and (S) enantiomers of the negatively charged chiral analytes with the positively charged quinine-derived chiral SO and on mobility differences of free and complexed SAs, so that differences in the overall migration behavior of the SA enantiomers result. To suppress problems associated with the high UV absorption of the chiral SO and thus the high detector background in the 'total filling technique', the 'partial filling technique' has been adopted. Several parameters including filling time and length of SO zone, respectively, SO concentration, type of background electrolyte, have been evaluated. Using such an optimized method, for example, (R) and (S) enantiomers of 2,4-dinitrophenyl (DNP)-protected proline could be separated with alpha=1.08, R(S)=6.60, and N=130,000 theoretical plates within 15 min. Similar alpha values, resolution, and efficiencies were observed for other DNP-protected, as well as for diverse, N-derivatized amino acids like N-benzoyl, N-9-fluorenylmethoxycarbonyl, N-3,5-dinitrobenzyloxycarbonyl amino acids. A repeatability study clearly validated the robustness of the method and revealed its practical applicability.
2. Synthesis of glycopeptides with phytoalexin elicitor activity--III. Syntheses of hexaglycosyl hexapeptides and a nonaglycosyl hexapeptide
T Takeda, T Kanemitsu, Y Ogihara Bioorg Med Chem. 1996 Nov;4(11):1873-80. doi: 10.1016/s0968-0896(96)00170-8.
A block synthesis of the model compound for the phytoalexin elicitor-active glycoprotein is described. Combination of the C-terminus free compounds, N-(9-fluorenylmethoxycarbonyl)-O-(tert-butyl)-L-seryl-L-proline (1) or N-(9-fluorenylmethoxycarbonyl)-(2,3,4,6-tetra-O-acetyl-beta-D-g luc opyranosyl) -(1-->6)-(2,3,4-tri-O-acetyl-alpha-D-mannopyranosyl)-(1-->6) -(2,3,4-tri-O-acetyl-alpha-D-mannopyranosyl)-L-seryl-L-proline (2) with the N-terminus free compounds, 2,3,4,6-tetra-O-acetyl-beta-D-glucopyranosyl -(1-->6)-(2,3,4-tri-O-acetyl-alpha-D-mannopyranosyl)-(1-->6)-(2,3,4-tri- O -acetyl-alpha-D-mannopyranosyl)-L-seryl-L-prolyl-L-seryl-L-proline methyl ester (4), O-(tert-butyl)-L-seryl-L-prolyl-(2,3,4,6-tetra-O-acetyl-beta-D -glucopyranosyl)-(1-->6)-(2,3,4-tri-O-acetyl-alpha-D-mannopyranosyl) -(1-->6)-(2,3,4-tri-O-acetyl- alpha-D-mannopyranosyl)-L-seryl-L-proline methyl ester (6) or 2,3,4,6-tetra-O-acetyl-beta-D- glucopyranosyl -(1-->6)-(2,3,4-tri-O-acetyl-alpha-D-mannopyranosyl)-(1-->6) -(2,3,4-tri-O-acetyl-alpha-D-mannopyranosyl)-L-seryl-L-prolyl -(2,3,4,6-tetra-O-acetyl-beta-D-glucopyranosyl)-(1-->6) -(2,3,4-tri-O-acetyl-alpha-D-mannopyranosyl)-(1-->6) -(2,3,4-tri-O-acetyl-alpha-D-mannopyranosyl)-L-seryl-L-proline methyl ester (8), by use of N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ) gave three hexaglycosyl hexapeptides and a nonaglycosyl hexapeptide derivatives (9, 11, 14, and 17). These N-terminus free compounds were derived from triglycosyl tetrapeptides (3 and 5) or a hexaglycosyl tetrapeptide (7) on selective deblock reaction by morpholine. The hexaglycosyl hexapeptides (10, 13, and 16) and the nonaglycosyl hexapeptide (18) have been prepared by the convergent block synthesis.
3. Syntheses of triglycosyl tetrapeptides and a hexaglycosyl tetrapeptide
T Takeda, T Kanemitsu, N Shimizu, Y Ogihara, M Matsubara Carbohydr Res. 1996 Mar 22;283:81-93. doi: 10.1016/0008-6215(96)00004-3.
A stereo-controlled synthesis of the model compound for the phytoalexin elicitor-active glycoprotein is described. Glycosylation of the trisaccharide, 2,3,4,6-tetra-O-acetyl-beta-D-glucopyranosyl-(1-->6)-2,3,4-tri-O-acetyl- alpha-D-mannopyranosyl-(1-->6)-2,3,4-tri-O-acetyl-alpha-D-mannopyranosyl trichloroacetimidate (12), with N-(9-fluorenylmethoxycarbonyl)-L-seryl-L- proline benzyl ester (3) or N-(carbobenzoxy)-L-seryl-L-proline methyl ester (4) by use of BF3. OEt2 gave the triglycosyl-seryl-proline derivatives. The N- as well as C-terminus of these triglycosyl dipeptides could be deblocked selectively to give compounds 14 and 16, which are versatile intermediates for the completion of model compound synthesis of glycopeptide. Triglycosyl tetrapeptides (18, 21) and hexaglycosyl tetrapeptide (23) have been prepared by the convergent block synthesis.
