The Crystal Structure of (2 R, 7 S, 10 R)-2,10-diamino-5,5,7-trimethyl-4,8-diazaundecanenickel (II) perchlorate

The structure of the title compound, a tricyclic Ni(II) tetra-amine complex has been determined from analysis of photographic X-ray data. The crystal system is orthorhombic, space group P2₁2₁2₁, with unit cell dimensions a = 9.802, b = 8.998, c = 24.378 Å. The Ni atom is square planar coordinated. The six-membered chelate ring has a chair conformation. One of the five-membered chelate rings has a distorted gauche (λ) conformation with the methyl substituent in an equatorial position, the other has an unsymmetrical gauche (δ) conformation with the methyl substituent axial.     

X-ray diffraction studies of diisotactic polymers of cis- and trans-2-butene oxides

Crystalline polymers derived from cis- and trans-2-butene oxides were studied by x-ray diffraction methods. X-ray fiber and powder photographs of poly(trans-2-butene oxide) were indexed by an orthorhombic unit cell with the dimensions a = 13.72 A., b = 4.60 A., and c (chain axis) = 6.90 A.; the space group is P2₁2₁2₁. The crystal structure of this polymer has been determined in projection. The chain has an erythro-diisotactic structure with -dl, dl- carbon sequences. The polymer has a nonplanar zigzag backbone with carbon and oxygen atoms of alternate monomer units lying nearly in a plane. Two chain molecules pass through the unit cell. The unit cell of poly(cis-2-butene oxide) is orthorhombic with lattice constants a = 11.20 A., b = 10.44 A., c (chain axis) = 7.01 A. The polymer has a threo-diisotactic structure with -dd,dd- or -ll,ll- carbon sequences. Four chain molecules pass through the unit cell. The crystal lattice is body-centered but the space group has not yet been established. The polymer has an almost fully extended zigzag chain configuration. Polymers prepared by either metal halide catalysts (FeCl₃, SnCl₄) or organometallic catalysts were essentially identical; the latter catalysts did, however, yield more highly crystalline polymers.     

Synthesis of the N-Amykitanosyl Tetramic Acid Moiety of Amycolamicin

An improved five-step synthetic route from l -fucose to an N-glycosyl l -valine methyl ester has been developed. The new route involves glycosidation of l -fucose with phenol in a β-selective manner without protection/deprotection steps and one-pot stereochemical inversion of a secondary alcohol intermediate and is superior to our previous one both in the number of steps and in overall yield. An N-glycosyl l -valine benzyl ester, prepared from l -fucose in an analogous way, has been elaborated into an N-amykitanosyl tetramic acid derivative, Li's synthetic intermediate for amycolamicin, via a four-step sequence which features the utilization of Bestmann's ylide to stereoconvergently construct an N-glycosyl tetramic acid intermediate in a single step, opening of a cyclic carbonate ring with an amine to regioselectively install a carbamate functionality, and visible light-mediated oxidative debenzylation of an N,N-dibenzyl carbamate.     

Modelisation of the Electric Field Linear Response of an Infinite Aggregate of All-Trans Hexatriene Chains by Electrostatic Interaction Model

A classical electrostatic polarization scheme using the additive distribution procedure has been applied to determine the longitudinal polarizability of an all-trans hexatriene molecule in an infinite stretched fiber. The parameters have been derived from ab initio CPHF/6-31G calculations and the electrostatic scheme has been validated via comparison with ab initio results on small clusters. Upon packing the polarizability of all-trans hexatriene increases by 7%. This small increase results from the balance between the enhancement of the polarizability due to collinear packing and the reduction associated with lateral packing.     

Tautomerism,protonation regioselectivity of 2-pyrrolidone and its complexation with palladium(II): an insight from the viewpoint of quantum chemistry

It has been established (AM1, PM3, RHF/6-31G**, MP2/6-31G**//RHF/6-31G**) that in the gaseous phase and in aqueous solution, the most thermodynamically stable tautomer of 2-pyrrolidone is lactame. According to PM3 evaluations with an explicit accounting for aqueous medium, the state of tautomeric equilibrium serves as a prerequisite to participation of 2-pyrrolidone's lactime tautomer (pyrroline-2-ol) in complexation with palladium(II) in aqueous solution. 2-Pyrrolidone protonation in the gaseous phase and in aqueous medium has been shown to proceed via the oxygen atom, corresponding to expectations on mesomeric displacement of electron density in the amide fragment. The aqueous medium stabilizes 2-pyrrolidone's lactime tautomer to a greater extent than for lactame, and an O-protonated cyclic amide compared to an N-protonated one. The stereodirective character of palladium(II) complexation with chloride ion and pyrroline-2-ol has been explained. The initially formed tetragonal–pyramidal adduct with an axial organic ligand rearranges into a precursor of the cis product, an intermediate with an extra coordinated axial chlorine atom. The less thermodynamically stable cis isomer of [PdCl₂(pyrroline-2-ol)₂] appears because its precursor is a lower energy intermediate of associative nucleophilic substitution. At a supramolecular level, cis product is capable of being stabilized by means of intermolecular dipole–dipole association in a crystal.     

Gas-Phase Molecular Structure of 2-Halo-1,3-dihetero-2-phospholanes

The molecular structure of 2-chloro-1,3-dithia-2-phospholane was determined using gas-phase electron diffraction and ab initio calculations. The heteroring in the molecule has an asymmetric structure like a symmetric P-envelope twisted about the C-C bond with an axial P-Cl bond. Geometric parameters of the molecule and mean vibration amplitudes were determined. The molecular structure of 2-chloro-1,3-oxathia-2-phospholane was predicted. The molecule in the gas phase has two conformers [twisted C(O)- and C(S)-envelope] with an axial P-Cl bond.     

The kinetics of the deparotonation of tropaeolin O

The reaction between tropaeolin O and hydroxyl ions has been reinvestigated in the pH range between 10.8 and 12.2 at 25°C and an ionic strength I of 0.1 M, using the T-jump method. The rate constants obtained from results at pH ≥ 11.66 are in satisfactory agreement with previous data. At lower pH, however, the rate is found to increase with decreasing hydroxyl-ion concentration. A mechanism which is compatible with these results is proposed and discussed. The dissociation constant of the last proton at I=0.1 M has been redetermined and found to be in satisfactory agreement with values given in the literature.     

Synthesis of an L-Fucose-Derived Cyclic Nitrone and its Conversion to α-L-Fucosidase Inhibitors

The L -fuco-nitrone 1 has been synthesized from allyl 4,6-O-benzylidene-α-D -glucopyranoside ( 4 ) in 11 steps and an overall yield of 18%. The key step is the intramolecular alkylation of an intermediary 1,1-bis(hydroxylamine) derived from the tosyloxy oximes (E/Z)- 2 . The nitrone 1 has been transformed into the diamine 30 , the indolizidines 39 and 40 , the indolizidinones 34 and 35 , and the imidazole 44 , all inhibiting bovine epididymis α-L -fucosidase with IC₅₀ values between 105 nM and 240 μM .     

Graph factorization: A new mode of application of a vertex-alternation scheme

Linear chains where the vertex weights change sign alternantly but are equal in magnitude were able to be reduced to smaller chains by a procedure analogous to that given by Coulson and Rushbrooke. The algorithm for constructing the reduced chains has been stated and proved. The results have been utilized, in conjunction with McClelland's graph-factorization method using reflection (σ) planes, to reduce the HMO secular determinants of some chemical graphs to an extent beyond the ability of group theory. McClelland's σ-plane algorithm, used repetitively where possible, produces factors whose sizes (n_M) are equal to those (n_G) of the group-theoretic factor blocks. For linear polyacenes (LP ), however, a new observation has been made: If the LP has an even number of fused rings, n_M = n_G; but when the LP has an odd number of fused rings, McClelland's process is effective in further reduction, i.e., n_M < n_G. In any case, however, the vertex alternation procedure reported in the present paper brings about further reduction. To demonstrate the utility of the present method, a sample calculation of the LUMO eigenvector graph theoretically has been shown for p-benzoquinone and the result has been utilized to obtain an inductive effect HMO parameter of the methyl group from the charge-transfer bands of some molecular complexes of methylated p-benzoquinones.© 1993 John Wiley & Sons, Inc.     

A Spectrophotometric Study OE Zirconium Complexes of 4,5-Dihydroxyfluorescein

Zirconium (IV) ions form violet red complex with 4,5-dihydroxyfluorescein in fairly strong mineral acid medium. The reagent has been successfully applied as a metal indicator in the direct EDTA titration of zirconium. The complex formed by 4,5-dihydroxyfluorescein and zirconium ions has been studied spectrophotometrically in 0.1M HCl solution. It is found that when an excess of metal ion is present, a violet red colored complex with metal-ligand ratio of 1:1, (MR) is formed and when an excess of 4,5-dihydroxyfluorescein is present a 1:2 complex (MR₂) may be predominant. The 1:1 complex has maximum absorption at 510 mμ and the 1:2 complex has very low solubility and tends to precipitate out from the solution. Job's method, log-ratio method and gravimetric method were used to establish the composition of complexes. The apparent stability constant of the 1:1 complex is found to be log K_h = 4.46 or K_h = 2.9×10¹ at pH 1.2.     

Ab initioLCAO-MO-SCF calculation of the electrostatic molecular potential of chlorpromazine and promazine

The electrostatic potential V( r ) arising from the ab initio LCAO-MO-SCF wave functions of chlorpromazine (CPZ ) and promazine (PZ ) has been calculated and discussed. In this approximation, the most probable sites of attack and reaction paths of electrophilic reagents are pointed out and compared. The analysis of V( r ) shows that the phenothiazine group has strong nucleophilic properties which are influenced by the phenothiazine substituent and that the electrostatic reactivity of CPZ and PZ is decidedly different near the phenothiazine substituent and similar near the side chain N atom. The dependence of V( r ) on the accuracy of the wave function has also been discussed by comparing some ab initio results on pyrrole, pyrazole, and imidazole obtained with a large basis set with an ab initio minimum basis set and with CNDO calculations.     

Generation and Rearrangement of N,O‐Dialkenylhydroxylamines for the Synthesis of 2‐Aminotetrahydrofurans

A new diastereoselective route to 2‐aminotetrahydrofurans has been developed from N,O‐dialkenylhydroxylamines. These intermediates undergo a spontaneous C?C bond‐forming [3,3]‐sigmatropic rearrangement followed by a C?O bond‐forming cyclization. A copper‐catalyzed N‐alkenylation of an N‐Boc‐hydroxylamine with alkenyl iodides, and a base‐promoted addition of the resulting N‐hydroxyenamines to an electron‐deficient allene, provide modular access to these novel rearrangement precursors. The scope of this de novo synthesis of simple nucleoside analogues has been explored to reveal trends in diastereoselectivity and reactivity. In addition, a base‐promoted ring‐opening and Mannich reaction has been discovered to covert 2‐aminotetrahydrofurans to cyclopentyl β‐aminoacid derivatives or cyclopentenones.     

Computer Automated Structure Evaluation (CASE) of the teratogenicity of retinoids with the aid of a novel geometry index

Summary The CASE (Computer Automated Structure Evaluation) program, with the aid of a geometry index for discriminating cis and trans isomers, has been used to study a set of retinoids tested for teratogenicity in hamsters. CASE identified 8 fragments, the most important representing the non-polar terminus of a retinoid with an additional ring system which introduces some rigidity in the isoprenoid side chain. The geometry index helped to identify relevant fragments with an all-trans configuration and to distinguish them from irrelevant fragments with other configurations.     

The low‐temperature phase of di‐tert‐butylsilanediol

The crystal structure of di‐tert‐butyl­silanediol, C₈H₂₀O₂Si, has a reversible phase transition at 211 (2) K. The orthorhombic high‐temperature structure has space group Ibam, with Z′ = , and shows a disordered hydrogen‐bonding system. The low‐temperature structure, determined at 143 (2) K, has a twinned monoclinic cell, with space group C2/c and Z′ = 2, and shows an ordered hydrogen‐bonding system.     

LC with Novel Electrochemical Detection for Analysis of Monoamine Neurotransmitters in Rat Brain After Administration of (R)-Salsolinol and (R)-N-Methylsalsolinol

A novel electrochemical detector with an acetylcholine film has been developed for HPLC. The chemically modified electrode is an efficient electrocatalyst of (R)-salsolinol ((R)-Sal), (R)-N-methylsalsolinol ((R)-NMSal), and monoamine neurotransmitters, enabling highly sensitive detection. The electrode is also stable and long-lived. Combined with microdialysis sampling, HPLC with the novel detector enabled successful study of changes in the concentrations of monoamine neurotransmitters in rat brain after the injection of (R)-salsolinol and (R)-N-methylsalsolinol.     

CYP450 biosensors based on screen-printed carbon electrodes for the determination of cocaine

A new electrochemical method has been described and characterized for the determination of cocaine using screen-printed biosensors. The enzyme cytochrome P450 was covalently attached to screen-printed carbon electrodes. Experimental design methodology has been performed to optimize the pH and the applied potential, both variables that have an influence on the chronoamperometric determination of the drug. This method showed a reproducibility of 3.56% (n = 4) related to the slopes of the calibration curves performed in the range from 19 up to 166 nM. It has been probed the used of this kind of biosensors in the determination of cocaine in street samples, with an average capability of detection of 23.05 ± 3.53 nM (n = 3, α = β = 0.05).     

Low molecular weight by-products in the Ziegler polymerization of higher terminal olefins

For the polymerization of n-octadecene-1 with catalysts derived from titanium tetrachloride and triethylaluminum, it has been shown that, in addition to polymerization of the olefin, the formation of isomerized olefin occurs. The latter is predominantly trans-n-octadecene-2 and its formation is favored by increase in Al:Ti mole ratio, in catalyst concentration, and in reaction temperature. It has also been shown that 1,1-disubstituted ethylene is present in the nonpolymeric reaction products. The influence of added trans-n-octadecene-2 or trans-n-octadecene-7 on the polymerization of n-octadecene-1 has been studied, and it is shown that the 2-isomer has the more pronounced effect on polymer yield and intrinsic viscosity. It has also been shown that no significant copolymerization of terminal with nonterminal octenes or octadecenes occurs under these conditions. Results indicate that, in polymerizations of this kind, the interaction of catalyst with isomerized monomer is probably an important factor in determining polymer yield and molecular weight. The isomerization reaction is also of interest as a general preparative method for trans-2-olefins.     

Spectrophotometric Determination of Palladium with Methylthymol Blue

A new, sensitive spectrophotometric method for the determination of palladium(II) with methylthymol blue has been developed. The palladium methylthymol blue complex has an absorption maximum at 530 nm. The colour reaction has a sensitivity of 0.005 µg of palladium/cm² and obeys Beer's Law over the range 0.4 to 3.24 ppm of palladium. The effects of concentration of perchloric acid, reagent, heating, stability of colour and diverse ions have been investigated. The ratio of metal: ligand in the complex is 1:1 and the formation constant was calculated to be 1.18×10⁴.     

Intramolecular 6-endo-dig-Cyclization of Ethyl 5-Aminomethyl-4-(1,2,3-thiadiazol-4-yl)furan-2-carboxylate

The reaction of 5-aminomethyl-4-(1,2,3-thiadiazol-4-yl)furan-2-carboxylic acid ethyl ester with bases has given ethyl 5-sulfanylidene-4,5,6,7-tetrahydrofuro[2,3-c]pyridine-2-carboxylate as a result of intramolecular 6-endo-dig-cyclization of thioketene generated in situ with an internal CH₂NH₂ nucleophile. The obtained ester has been alkylated with iodomethane at the sulfur atom to form ethyl 5-methylsulfanyl-4,7-dihydrofuro[2,3-c] pyridine-2-carboxylate. The Hantzsch reaction with ω-bromoacetophenone has resulted in the formation of 7-ethoxycarbonyl-3-phenylfuro[3,2-d[1,3]thiazolo[3,2-a]pyridin-4-ium bromide.

     

Photoelimination reactions of N-heteroaromatic compounds

N-Heteroaromatic compounds substituted with a side chain next to the nitrogen and bearing a hydrogen gamma to the ring, undergo a photoelimination reaction to yield the methyl-substituted heterocycle and an alkene (if the gamma hydrogen is on a side chain carbon) or an aldehyde (if the gamma hydrogen is on a side chain oxygen). The reaction has been shown to occur with substituted isoquinolines, plienanthridines, pyridines and pyrazines.