Gerard N. Wagenaars

Synthesis of Fragments of the Capsular Polysaccharide of Haemophilus Influnzae Type B Part II. Preparation and Structural Analysis of Fragments Comprising two and Three Repeating Units

Abstract The synthesis of spacer-containing fragments of the capsular poly-saccharide of H. influenzas, comprising two and three repeating units (9a and 9b, respectively), is presented. Ribosylribitol building blocks 1 and 2 were coupled with bis [1-benzotriazolyl]-2-chlorophenyl phosphate (3) to give the phosphotriester derivative 5a (72%), which was selectively deprotected at O-5 of the terminal ribitol residue (cleavage of the trans-1-propenyl ether) to afford compound 6a (82%). Repeated coupling of building block 2 with 6a (chain elongation), followed by propenyl- cleavage, gave analogue 6b. Both derivatives 6a and 6b were coupled with spacer 7 (chain termination). The fully protected fragments 8a (84%) and 8b (49%, starting from 6a) were thus obtained. Complete deprotection of 8a and 8b was achieved in three steps. After purification and cation-exchange, 9a and 9b were obtained in 41 and 68% yields, respectively. The structural integrity of the largest fragment (9b) was confirmed by FAB MS and variou...

The discrimination between human, porcine and bovine insulin with 1H NMR spectroscopy

Abstract— The 1H‐ and 1H‐1H correlation (COSY) NMR spectra of human, porcine and bovine insulin have been recorded. The 1.1–1.5 ppm regions of these spectra show the methyl signals of the alanine and threonine residues. The number of alanines and threonines differs for the three insulins and thus allows an easy discrimination with NMR.

Peptide backbone-to-backbone cyclisation as an avenue to β-turn mimics

Abstract 1,3-Dipolar cycloaddition of the nitrone functionality of 13 and the alkene functionality of 8 yields the backbone-to-backbone cyclised peptides 14–16. The conformation of these structures is such that they are β-turn mimics. They differ in their C3 C5 stereochemistry with discrete conformational differences.

Tritium nuclear magnetic resonance spectroscopy of [Pyrrolidine-3H]bepridil

Bepridil [N-benzyl-3-isobutoxy-N-phenyl-2-(pyrrolidin-1-yl)propylamine] tritiated in the pyrrolidine ring by reduction of the 2,5-dihydropyrrol-1-yl analogue with tritium shows a complicated 1H-decoupled 3H n.m.r. spectrum. With the aid of isotopic fractionation by h.p.l.c. this spectrum could be interpreted as a sum of the spectra of various mono-, di-, and tri-tritiated diastereoisomers. In the case of the (+)-(R)-isomer of bepridil the optical purity could be determined by 3H n.m.r. in the presence of Pirkles alcohol.

14 C isotope effects in 1H and 13C n.m.r. spectroscopy

Replacement of 12C by 14C induces small upfield shifts of the directly bonded 1H and 13C nuclei; these shift differences can be used to measure the extent of 14C labelling.