Measurement of the charged pion electromagnetic form factor

Separated longitudinal and transverse structure functions for the reaction 1H(e,e(')pi(+))n were measured in the momentum transfer region Q2 = 0.6--1.6 (GeV/c)(2) at a value of the invariant mass W = 1.95 GeV. New values for the pion charge form factor were extracted from the longitudinal cross section by using a recently developed Regge model. The results indicate that the pion form factor in this region is larger than previously assumed and is consistent with a monopole parametrization fitted to very low Q2 elastic data.     

Asymmetric synthesis of novel thioiso dideoxynucleosides with exocyclic methylene as potential antiviral agents

Novel thioiso pyrimidine and purine nucleosides substituted with exocyclic methylene have been synthesized, starting from D-xylose. The glycosyl donor 14 was synthesized from D-xylose, using cyclization of dimesylate 10 with sodium sulfide as a key step. Cyclization proceeded in pure S(N)2 reaction without going through S(N)1 reaction in the presence of an allylic functional group at low reaction temperature (0 degrees C) in polar solvent (DMF), affording compound 12 as a major product. At higher temperatures, S(N)2' product 11 was almost exclusively obtained as a major product. On the other hand, glycosylation of 14 with 6-chloropurine under Mitsunobu conditions afforded the desired S(N)2 product 26, while palladium-catalyzed glycosylation resulted in the sole formation of S(N)2' product 34.     

Facile synthesis of thiacalix[n]arenes (n=4, 6, and 8) consisting of p-tert-butylphenol and methylene/sulfide alternating linkage and metal-binding property of the n=4 homologue

2,14-Dithiacalix[4]arene 3₄ was conveniently prepared in 16% yield by acid-catalyzed cyclocondensation of 2,2^′-thiobis[4-tert-butylphenol] with formaldehyde. The present method also afforded the first isolation of the analogues with six and eight phenol units, 3₆ (10%) and 3₈ (5%), respectively. Solvent extraction showed that 3₄ had high selectivity toward Cu²⁺ ion at pH 5.5 by coordination of the bridging sulfur with cooperative donation of the adjacent phenolate oxygens.     

Novel receptor surface approach for 3D-QSAR: the weighted probe interaction energy method

A 3D-QSAR technique, called the WeP (weighted probe interaction energy) method, has been developed based on the notion that certain regions of the receptor surface contribute, to varying extents, to the differences in the activities of the ligands, while other regions do not. The probes, placed around the surface of a superimposed set of ligands, were associated with fractional weights, and then an optimal distribution of probe weights that accounts for the activity profile of the training ligands was determined using a genetic algorithm. It has been shown for the three test samples that the pseudoreceptors, which consist of the surviving probes with nonzero weight values, have good predictabilities. Especially, in the case of dihydrofolate reductase inhibitors, the pseudoreceptor resembles the real protein in that there is no surviving probe in the solvent-exposed region.     

Total synthesis of (+)-SCH 351448

Total synthesis of SCH 351448 was accomplished employing the ring-closing olefin metathesis reaction for the preparation of the 28-membered macrodiolide.