Synthesis of dl-cis- and (4R,5R)-trans-7-[2,2-dimethyl-4-(phenylsulfonyl)-aminomethyl-1,3-dioxolan-5-yl]-5(Z)-heptenoic acid analogues as platelet thromboxane A2 receptor antagonist

Investigation of diastereoselective acyclic α-alkoxydithioacetal substitutions involving thiacarbenium intermediates

Reported herein is an experimental and theoretical study that elucidates why silylated nucleobase additions to acyclic α-alkoxythiacarbenium intermediates proceed with high 1,2-syn stereocontrol (anti-Felkin-Anh), which is opposite to what would be expected with corresponding activated aldehydes. The acyclic thioaminals formed undergo intramolecular cyclizations to provide nucleoside analogues with anticancer and antiviral properties. The factors influencing the selectivity of the substitution reaction have been examined thoroughly. Halothioether species initially form, ionize in the presence (low dielectric media) or absence (higher dielectric media) of the nucleophile, and react through SN2-like transition structures (TS A and D), where the α-alkoxy group is gauche to the thioether moiety. An important, and perhaps counterintuitive, observation in this work was that calculations done in the gas phase or low dielectric media (toluene) are essential to locate the product- and rate-determining transition structures (C-N bond formation) that allow the most reasonable prediction of selectivity and isotope effects for more polar solvents (THF, MeCN). The ΔΔG(⧧) (G(TSA-TSD)) obtained in silico are consistent with the preferential formation of 1,2-syn product and with the trends of stereocontrol displayed by 2,3-anti and 2,3-syn α,β-bis-alkoxydithioacetals.

Hydrogen bond interactions of a series of N-substituted TXA2 receptor antagonists

A series of N-substituted sulphonamide based thromboxane A2 (TXA2) receptor antagonists were synthesised with the objective to explore the role of hydrogen bond donation properties in the binding of these ligands to the TXA2 receptor. Pharmacological evaluation of these compounds revealed that the binding affinity decreased significantly with the removal of the hydrogen bond donor. This indicates that a hydrogen bond donor is important for the binding of these antagonists to the TXA2 receptor.

The biogenetic anatomy of vitamin B6. A 13C NMR investigation of the biosynthesis of pyridoxol in Escherichia coli

It is shown by incorporation experiments with 13C bond-labeled substrates, followed by analysis by means of 13C NMR spectroscopy, that two compounds, 1-deoxy-D-xylulose (12) and 4-hydroxy-L-threonine (), serve as precursors of pyridoxol (vitamin B6) (1) in Escherichia coli. Together, these two compounds account for the entire C8N skeleton of the vitamin. 1-Deoxy-D-xylulose supplies the intact C5 unit, C-2',2,3,4,4' of pyridoxol. 4-Hydroxy-L-threonine undergoes decarboxylation in supplying the intact C3N unit, N-1,C-6,5,5'. Both precursors are ultimately derived from glucose. The C5 unit of pyridoxol that is derived from 1-deoxy-D-xylulose originates by union of a triose phosphate (yielding C-3,4,4') with pyruvic acid (which decarboxylates to yield C-2',2). D-Erythroate (11) enters the C3 unit, C-6,5,5', and is therefore an intermediate on the route from glucose into 4-hydroxy-L-threonine.