Highly regioselective hydrolysis of tricarballylates (“retro-fats”) and citrates by subtilisin

Trimethyl and triethyl esters of tricarballylic acid and citric acid were hydrolysed with porcine liver esterase(PLE) to the isomeric diesters. In all cases the hydrolysis took place with poor regioselectivity (maximum 50% excess). However, the hydrolysis of trimethyl and triethyl esters of tricarballylic acid and of the triethyl ester of citric acid with subtilisin was absolutely regioselective and the symmetric 1,5-diester was obtained.     

Two new C-methylated flavonoids from Myrica gale

From the leaves of Myrica gale 2′,4′-dihydroxy-6′-methoxy-3′,5′-dimethylchalcone has been isolated. The fruits yielded 2′-hydroxy-4′,6′-dimethoxy-3′-methyldihydrochalcone. The constitutions were deduced from spectroscopic data and confirmed by synthesis.     

Structures of the pleiotropic translational regulator Hfq and an Hfq-RNA complex: a bacterial Sm-like protein

In prokaryotes, Hfq regulates translation by modulating the structure of numerous RNA molecules by binding preferentially to A/U-rich sequences. To elucidate the mechanisms of target recognition and translation regulation by Hfq, we determined the crystal structures of the Staphylococcus aureus Hfq and an Hfq-RNA complex to 1.55 and 2.71 A resolution, respectively. The structures reveal that Hfq possesses the Sm-fold previously observed only in eukaryotes and archaea. However, unlike these heptameric Sm proteins, Hfq forms a homo-hexameric ring. The Hfq-RNA structure reveals that the single-stranded hepta-oligoribonucleotide binds in a circular conformation around a central basic cleft, whereby Tyr42 residues from adjacent subunits stack with six of the bases, and Gln8, outside the Sm motif, provides key protein-base contacts. Such binding suggests a mechanism for Hfq function.     

Enantiopure derivatives of 1,2-alkanediols: substrate requirements of lipase B from Candida antarctica

Efficient methods for kinetic resolution of 1-phenoxy-2-butanol, 1-phenylmethoxy-2-butanol, and 1-phenoxy-2-pentanol were developed using lipase B from Candida antarctica as catalyst. Resolutions were performed in order to investigate the substrate requirements needed to obtain a high E-value. The effect of the substrate structure on E is different for transesterifications in organic media as compared to hydrolysis. The influence of different acyl donors on the E-value was also investigated.     

Synthesis and 1H NMR studies of 3-(D-erythro-glycerol-1-yl)-1H-pyrazolo[3,4-b]quinoxaline and its 7-chloro and 7-methyl analogues

3-(D-erythro-Glycerol-1-yl)-1H-pyrazolo[3,4-b]quinoxaline and its 7-chloro and 7-methyl analogues (11 and 12) were prepared from the corresponding quinoxalines. The 7-substituted analogues 11 and 12 were obtained as the preponderant isomers, and the 6-substituted analogues as the minor isomers. The structure and position of the substituent were determined by 1H NMR studies. The effect of substitution on the chemical shift of other protons is discussed.     

2-C-Methyl-d-erythritol. Produced in plants,forms aerosols in the atmosphere. An alternative pathway in isoprenoid biosynthesis

2-C-Methyltetritols, or 2-methyl-1,2,3,4-butanetetraols, which exist as four stereoisomers, are found to be present in the atmosphere above the Amazonian rainforest. 2-C-methyl-d-erythritol was originally isolated from Convolvulus glomeratus and later synthesized enantiomerically pure. It has been claimed that these compounds are produced from isoprene by radical oxidation in the atmosphere. More recently, detailed analysis has shown that the mixture of stereoisomers from forests in both Brazil and Sweden contains unequal amounts of enantiomers. This shows that the oxidation must be due to enzymatic activity in plants. A review of the history of these compounds, synthesis and the significance of stereochemistry is given. Moreover, the significance of 2-C-methyl-d-erythritol for the non-mevalonate route to isoprenoids is briefly discussed.