A range of 13 C-labeled carbohydrates containing C-O-C-C coupling pathways having different structures and dihedral angles has been prepared and used to identify structural factors affecting 3 J COCC , especially those across the O-glycosidic linkages of oligosaccharides. Model mono-and disaccharides were geometrically optimized using density functional methods, and scalar couplings involving carbon were calculated using a similar approach coupled with finite-field perturbation theory. Experimental and calculated 3 J COCC values were in close agreement, thus allowing use of the latter to better define the effect of carbohydrate structure on 3 J COCC magnitude. In addition to dihedral angle, the disposition of terminal electronegative substituents along the C-O-C-C coupling pathway significantly affects 3 J COCC values, and structural motifs have been identified where these effects may be encountered in oligosaccharides. A simple Karplus equation for trans-O-glycoside 3 J COCC values is proposed and has been applied in the reanalysis of trans-O-glycosidic couplings in 13 Clabeled methyl β-lactoside and sucrose. The behavior of trans-O-glycosidic 2 J COC and 3 J COCH values, which provide structural information complementary to that derived from 3 J COCC values, is also discussed.

Methyl alpha- and beta-pyranosides of d-glucose and d-galactose 1-4 were prepared containing single sites of (13)C-enrichment at C4, C5, and C6 (12 compounds), and (1)H and (13)C[(1)H] NMR spectra were obtained to determine a complete set of J-couplings ((1)J, (2)J, and (3)J) involving the labeled carbon and nearby protons and carbons within the exocyclic hydroxymethyl group (CH(2)OH) of each compound. In parallel theoretical studies, the dependencies of (1)J, (2)J, and (3)J involving (1)H and (13)C on the C5-C6 (omega) and C6-O6 (theta;) torsion angles in aldohexopyranoside model compounds were computed using density functional theory (DFT) and a special basis set designed to reliably recover the Fermi contact contribution to the coupling. Complete hypersurfaces for (1)J(C5,C6), (2)J(C5,H6)(R), (2)J(C5,H6)(S), (2)J(C6,H5), (2)J(C4,C6), (3)J(C4,H6)(R), (3)J(C4,H6)(S), and (3)J(C6,H4), as well as (2)J(H6)(R)(,H6)(S), (3)J(H5,H6)(R), and (3)J(H5,H6)(S), were obtained and used to parametrize new equations correlating these couplings to omega and/or theta;. DFT-computed couplings were also tested for accuracy by measuring J-couplings in (13)C-labeled 4,6-O-ethylidene derivatives of d-glucose and d-galactose in which values of omega and theta; were constrained. Using a new computer program, Chymesa, designed to utilize multiple J-couplings sensitive to exocyclic CH(2)OH conformation, the ensemble of experimental couplings observed in 1-4 were analyzed to yield preferred rotamer populations about omega and theta;. Importantly, due to the sensitivity of some couplings, most notably (2)J(H6)(R)(,H6)(S), (2)J(C5,H6)(R), and (2)J(C5,H6)(S), to both omega and theta;, unique information on correlated conformation about both torsion angles was obtained. The latter treatment represents a means of evaluating correlated conformation in 1,6-linked oligosaccharides, since psi and theta; are redundant in these linkages. In the latter regard, multiple, redundant scalar couplings originating from both sides of the glycosidic linkage can be used collectively to evaluate conformational correlations between psi/theta; and C5-C6 bond rotamers.

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A liquid chromatographic method for the determination of artemisinine in human plasma and saliva is described. Artemisinine was extracted from plasma and saliva samples with ethyl acetate and then converted to a strongly UV-absorbing compound, Q260, by a known pre-column reaction. The samples were chromatographed on a C18 column with a 0.010 M NaH2P04 -Na2HP04 buffer solution (watermethanol = 6 + 4) as the mobile phase. The purity and identity of the peaks of interest were examined. The detection limit of artemisinine in plasma and saliva was about 2.5 ng ml-1. Over the concentration range 10-1000 ng ml-1, the recovery and relative standard deviation were ~9 5 % and 1.2-18%, respectively. Plasma and saliva concentration -time profiles were determined in two healthy volunteers after the administration of a rtem isi n i ne.