Jan-Remt Mellema

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.

Conformational aspects of malic acid: A multidisciplinary approach

Malic acid molecules can adopt three different staggered conformations of minimum energy with respect to rotation around the central C-C bond: gauche - (g- ), trans (t) and gauche + (g+ ). The conformational behaviour of the acid and of its dissociated forms has been studied by means of NMR experiments and Molecular Dynamics simulations and the results are compared with a statistical analysis of crystal structures and with Molecular Mechanics calculations. Specific coupling constants for all three ionization states were determined. Coupling constants of the three staggered rotamers were calculated and by comparison with the specific coupling constants of each ionization state rotamer populations were determined. Observed and calculated populations are similar, although the gauche + population resulting from the NMR experiment is significantly higher than predicted by the other methods. All techniques indicate that gauche + is the minor conformer of the neutral molecule. It is also shown that water-acid interactions play a very important role in describing the conformational behaviour of malic acid properly.