Structure of asperketal B

3,7,11-Trimethyl-13-oxabicyclo[8.3.0]trideca-2,6-diene-12-spiro-2' -(5',5'-dimethyltetrahydrofuran), asperketal B, C20H30O2, M(r) = 302.46, orthorhombic, P2(1)2(1)2(1), a = 10.064(1), b = 22.214(2), c = 8.330 (1) A, V = 1862.3 A3, Z = 4, Dx = 1.08 g cm-3, Cu K alpha, lambda = 1.54178 A, mu = 4.55 cm-1, F(000) = 664, T = 294 (1) K, R = 0.031, wR = 0.027 for 953 data. The backbone of the molecule is composed of a cyclodecadiene ring which is cis fused to a bicyclic ketal system. The relative configurations at C(1), C(10), C(11) and C(12) are 1S*, 10R*, 11R* and 12R*.

Structure of 1,1-dichloro-2-(4-methoxyphenyl)-2,3-diphenylcyclopropane

C22H18Cl2O, M(r) = 369.3, monoclinic, P2(1)/a, a = 16.585(1), b = 17.328(1), c = 13.192(3) A, beta = 107.443(8) degrees, V = 3616.8 A3, Z = 8, Dx = 1.356 g cm-3, lambda(Mo K alpha) = 0.71069 A, mu = 3.2 cm-1, F(000) = 1536, T = 138 K, R = 0.039 for 5450 observed reflections. The structural features of the two independent molecules are quite similar except in the orientation of the methoxy group. The cyclopropane ring shows the expected bond-length asymmetry with C(2)-C(3) as the longest bond. The two cis-arranged phenyl rings adopt similar conformations as observed in diaryl-cyclopropanes, with one ring in the bisecting position and the other near the perpendicular position. The conformation of the third aryl ring is also near the perpendicular position. The overall conformation of the three aryl rings is different from the helical propeller conformation consistently observed in tamoxifen and all other known tri(tetra)aryl-vinyl systems.

Contribution of tyrosine 6 to the catalytic mechanism of isoenzyme 3-3 of glutathione S-transferase

The role of the hydroxyl group of tyrosine 6 in the catalytic mechanism of isoenzyme 3-3 of rat glutathione S-transferase has been examined by x-ray crystallography and site-specific replacement of the residue with phenylalanine and evaluation of the catalytic properties of the mutant enzyme. This particuar tyrosine residue is conserved in the sequences of all of the cytosolic enzymes and is found, in crystal structures of both isoenzyme 3-3 from the mu-gene class and an isoenzyme from the pi-gene class, to be proximal to the sulfur of glutathione (GSH) or glutathione sulfonate bound at the active site. The 2.2-A structure of the binary complex of isoenzyme 3-3 and GSH indicates that the hydroxyl group of Tyr6 is located 3.2-3.5 A from the sulfur of GSH, well within hydrogen bonding distance. Removal of the hydroxyl group of Tyr6 has essentially no effect on the dissociation constant (22 +/- 3 microM) for GSH. Nevertheless the Y6F mutant exhibits a turnover number which is only about 1% that of the native enzyme when assayed at pH 6.5 with either 1-chloro-2,4-dinitrobenzene (CDNB) or 4-phenyl-3-buten-2-one. UV difference spectra of the binary enzyme-GSH complexes suggest that the predominant ionization state of GSH in the active site of the Y6F mutant is the neutral thiol (e.g. EY6F.GSH) which is in contrast to the native enzyme in which the thiol is substantially deprotonated (e.g. E.GS-). Spectrophotometric titration suggests that the pKa of the thiol is 6.9 +/- 0.3 in the E.GSH complex and greater than or equal to 8 in the EY6F.GSH binary complex. In addition, the pH dependence of kcat/KmCDNB reveals that the reactions catalyzed by the native enzyme and the Y6F mutant are dependent on a single ionization in the E.GSH and EY6F.GSH complexes with pKa = 6.2 +/- 0.1 and 7.8 +/- 0.3, respectively. The results suggest that the hydrogen bond between Tyr6 and the enzyme-bound nucleophile helps to lower the pKa of GSH in the binary enzyme-substrate complex.

Changes of nerve excitability and urinary deltamethrin in sprayers

The nerve excitability of median nerve as well as the urinary deltamethrin and its metabolite dibromovinyl-dimethyl-cyclopropane carboxylic acid (Br2A) were detected in 24 deltamethrin sprayers in an assessment of the exposure and effect of deltamethrin. Twenty-nine male, unexposed referents of the same age range were also selected. The urinary deltamethrin and its metabolite Br2A were detectable by GC and HPLC in the sprayers after exposure. The nerve excitability detected with an electromyograph and pairs of stimuli at variable intervals showed that there was a prolongation of supernormal period in median nerve of the exposed group after a 3-d spraying compared with that before spraying which became more significant 2 d after cessation of exposure. In the mean time, no change of supernormal period in the median nerve of reference group was found at the 3-d interval. Nearly half of the sprayers had a supernormal period prolonged by more than 4 ms after spraying, whereas nearly none of the reference group showed similar changes after repeated examinations. Although there was neither correlation between the nerve excitability changes and the urinary deltamethrin or Br2A excretion, nor was a case of acute deltamethrin poisoning diagnosed, the non invasive technique used for nerve excitability detection in this study seems to be valuable in studying deltamethrin toxicity on human.

The structures of different diastereomers of bicyclo[2.2.1]hept-5-en-2-yl phenyl sulfoxide

Three diastereomers of bicyclo[2.2.1]hept-5-en-2-yl phenyl sulfoxide were prepared by Diels-Alder [4 + 2] cycloadditions between phenyl vinyl sulfoxide and cyclopentadiene. The isomers were separated by column chromatography on silica gel and repeated recrystallizations gave the pure racemates of three of the four possible diastereomers. It proved to be impossible to assign the stereochemistry of the products from low-resolution NMR spectra. The X-ray diffraction studies of the three diastereomers showed the relative configuration at the two chiral centers and these stereochemical assignments were, subsequently, correlated with the two-dimensional NMR spectroscopic results. Compound (I), exo-(2R*,8S*)-bicyclo[2.2.1]hept-5-en-2-yl phenyl sulfoxide [or the exo-(2S*,8R*)-isomer], C13H14OS, Mr = 218.31, orthorhombic, P2(1)2(1)2(1), a = 10.517 (2), b = 10.914 (2), c = 9.642 (3) A, V = 1106.7 A3, Z = 4, Dx = 1.31 g cm-3, Cu K alpha, lambda = 1.54178 A, mu = 22.14 cm-1, F(000) = 464, T = 138 (2) K, R = 0.042 for 1151 data. Compound (II), exo-(2RS,8RS)-bicyclo[2.2.1]hept-5-en-2-yl phenyl sulfoxide, C13H14OS, Mr = 218.31, triclinic, P1, a = 8.775 (4), b = 16.353 (8), c = 7.804 (3) A, alpha = 90.67 (3), beta = 101.08 (4), gamma = 85.64 (5) degrees, V = 1095.8 A3, Z = 4, Dx = 1.32 g cm-3, Mo K alpha, lambda = 0.71069 A, mu = 2.18 cm-1, F(000) = 464, T = 138 (2) K, R = 0.062 for 3264 data. The two molecules in the asymmetric unit are crystallographically independent, but their conformations are similar.(ABSTRACT TRUNCATED AT 250 WORDS)