Synthesis and Diels-Alder Reactions of a New Kind of Chiral Dienophiles: Cyclic Vinyl-p-tolylsulfilimines

A new kind of chiral dienophiles, cyclic vinyl-p-tolylsulfilimines (2a and 2b), were obtained from the corresponding (Z)-sulfinylacrylonitriles with HBF(4) and methanol. The asymmetric Diels-Alder reaction of optically pure 2a with cyclopentadiene under mild thermal or catalyzed conditions afforded only the endo-4a adduct with complete endo and pi-facial selectivities. The ability of the sulfilimine moiety to enhance the dienophilic reactivity of the double bond is similar to that of the sulfinyl group.     

Acid-Catalyzed Rearrangement of 3-Aza-8-oxatricyclo[3.2.1. 02,4]octan-6-one Acetals. Highly Stereoselective Total Synthesis of 3-Amino-3-deoxy-D-altrose and Derivatives

Ethyl and tert-butyl azidoformate added to 7-oxabicyclo[2.2.1]hept-5-en-2-one dimethyl ( 5 ) and dibenzyl ( 6 ) acetals to give mixtures of regioisomeric triazolines. The latter gave the corresponding aziridines (6,6-dialkoxy-3-aza-8-oxatricyclo[3.2.1.0^2,4]octane-3-carboxylates 15 , 19 , 23 , and 27 and 31 ) on UV irradiation. In the presence of protic acids, the aziridines were rearranged into protected amines ([3-endo-alkoxy-5-oxo-7-oxabicyclo[2.2.1]hept-2-exo-yl]carbamates 16 , 20 , 24 , and 28 and 33 ). Using (+)-(1R, 4R)-5,5-bis(benzyloxy)7-oxabicyclo[2.2.1]hept-2-ene((+)- 6 ) derived from furan and l-cyanovinyl (1S)-camphanate, the method was applied to prepare 2-O-benzyl-3-[(tert-butoxy)carbonyiamino]-5-O-(3-chlorobenzoyl)-3-deoxy-β-D -altrofuranurono-6,1-lactone ((?)- 37 ). This compound was converted to methyl 3-amino-3-deoxy-α-D-altropyranoside hydrochloride ( 44 ) and several derivatives.     

Structure-Lipophilicity Relationships of Neutral and Protonated β-Blockers,Part I,Intra- and Intermolecular Effects in Isotropic Solvent Systems

The objectives of this study were to validate new experimental techniques used to measure the log P of protonated drugs, and to investigate the inter- and intramolecular forces influencing the partitioning behavior of β-blockers in isotropic biphasic solvent systems. The lipophilicity parameters of a number of β-blockers were measured by two-phase titration, centrifugal partition chromatography (CPC), and cyclic voltammetry (CV) in one or more of the following solvent systems: octanol/water, 1,2-dichloroethane/water, and dibutyl ether/water. CV proved to be a promising technique for measuring the lipophilicity of protonated β-blockers. Derived parameters such as Δlog P (difference between log P in two different solvent systems, a parameter valid for a given solute in a given electrical form) and diff (difference between log P of two different electrical forms of a given solute, in the same system) yielded insights into inter- and intramolecular interactions characteristic of β-blockers. The relevance of these parameters in structure-permeation relationships is explored.     

Zeros of the Whittaker function associated to Coulomb waves

The zeros in the complex z plane of the Whittaker function W_c/z,µ(z),closely related to spherical waves in the quantum-mechanicalCoulomb problem, are investigated for varying real values ofthe parameters c and µ     

Synthesis and evaluation of aminocyclopentitol inhibitors of beta-glucosidases

[reaction: see text] (1R,2S,3S,4R,5R)-4-Amino-5-(hydroxymethyl)cyclopentane-1,2,3-triol 1, prepared from D-glucose, inhibits beta-glucosidases from Caldocellum saccharolyticum (Ki = 1.8 x 10(-7) M) and from almonds (Ki = 3.4 x 10(-6) M). Inhibition is not influenced by N-ethylation (--> 15) but is strongly reduced upon N-acetylation (--> 12). Inversion of stereochemistry at C(5) (--> 14) has little effect on inhibition of beta-glucosidases. These experiments suggest that 1 acts as an analogue of a protonated beta-glucoside.     

Coupled fluid-structure interaction analysis

A general-purpose fluid-structure interaction capability which can be used in analyzing internal acoustic problems in automobiles and aircraft has been formulated. This capability has become an important issue in the last few years because of the emphasis that has been placed on noise control in all vehicles. A variety of output features that are needed by the analyst in identifying the causes of the acoustic problems have been studied and implemented. The fluid (air) is modeled as an inviscid, irrotational fluid with pressure variables as the degrees of freedom. An acoustic absorber element and an acoustic barier element are also implemented.     

Sur la composition de l'arôme de cacao

A gas-chromatographic separation of cocoa aroma, followed by infra-red and mass-spectrometric identification, has yielded, besides 22 of the 91 previously described constituents, 35 new substances (8 aliphatic, 1 alicyclic, 7 aromatic, 9 o-heterocyclic, 4 pyrrolic, and 6 pyrazinic).     

Zinc-proline catalyzed pathway for the formation of sugars

Zn-proline catalyzes the aldolisation of unprotected glycolaldehyde in water to give tetroses and hexoses; threose (33% of the product mixture) was formed with 10% enantiomeric excess of the D-isomer.