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Masood Parvez

Publications and source records attributed to Masood Parvez.

At least 37 records · Page 2Linked to original sources
PubMed2005

7:8,9:10-dibenzo-1,2,3,4-tetrafluoro- triphenylene: synthesis, structure, and photophysical properties of a novel [5]helicene.

A simple and efficient synthesis and crystallographic analysis of the partially fluorinated 7:8,9:10-dibenzo-1,2,3,4-tetrafluorotriphenylene, 1, in 59% yield is reported. Compound 1 is a blue luminescent [5]helicene in both solution and the solid state. It spontaneously forms enantiomorphous single crystals from racemic samples and exhibits slipped, face-to-face F...C(pi) contacts within the stacks of molecules.

Crystallography, X-Ray↗
PubMed2005

Formation of N-I charge-transfer bonds and ion pairs in polyiodides with imidotellurium cations.

[((t)BuNH)Te(mu-N(t)Bu)(2)Te(N(t))Bu)][OSO(2)CF(3)] (4a) is obtained in quantitative yields by the treatment of [((t)BuN)Te(mu-N(t)Bu)(2)Te(N(t)Bu)] (1) with HCF(3)SO(3). The reaction of 4a with LiI and iodine in the molar ratio 1:1:4.5 affords a product that, upon recrystallization from acetonitrile, was found to be a solid solution of [((t)BuNH)Te(mu-N(t)Bu)(2)Te(N(t)Bu)](2)I(20) (5a) and [((t)BuNH)Te(mu-N(t)Bu)(2)Te(NH(t)Bu)](2)I(18) (5b). Consequently, the crystal structure is disordered, containing 88.3(1)% of 5a.2MeCN and 11.7(1)% of 5b.2MeCN. The I(20) framework is involved in two symmetry-equivalent N-I-I-I-I fragments, two I(3)(-) ions, and three I(2) molecules that are linked together by I...I secondary bonding interactions. The bonding in the N-I-I-I-I fragment can be considered in terms of the lp(N) --> sigma*(I(2)) and pi(I(2)) --> sigma*(I(2)) charge-transfer interactions involving one [((t)BuNH)Te(mu-N(t)Bu)(2)Te(N(t)Bu)](+) cation and two I(2) units. The N-I bond length of 2.131(7) A, the I-I distances of 3.118(1), 3.095(2), and 2.788(2) A, and the angle I(2)-I(2) angle of 84.75(4) degrees are consistent with this bonding scheme. The I-I bond distances in the two symmetry-equivalent I(3)(-) ions are 3.113(1) and 2.792(2) A, and those in two crystallographically independent I(2) molecules are 2.736(2) and 2.743(1) A. The formal I(18)(4)(-) anion in 5b.2MeCN consists of four I(3)(-) anions and three I(2) molecules linked by I...I secondary bonds. One crystallographically independent I(3)(-) anion is connected to the [((t)BuNH)Te(mu-N(t)Bu)(2)Te(HN(t)Bu)](2+) cation by two hydrogen bonds [H...I = 2.823(5) and 2.983(5) A; N...I = 3.697(8) and 3.857(9) A]. The I(3)(-) anions and I(2) molecules in 5b show virtually identical bond parameters to those in 5a. The treatment of 1 with iodine and the reactions of its methylated derivatives, [((t)BuNMe)Te(mu-N(t)Bu)(2)Te(N(t)()Bu)][OSO(2)CF(3)] and [((t)BuNMe)Te(mu-N(t)Bu)(2)Te(MeN(t)Bu)][OSO(2)CF(3)](2), with LiI and iodine also afford highly moisture-sensitive polyiodides, either by the formation of N-I charge-transfer complexes or by ionic interactions. The crystal structures of the partially hydrolyzed products, [((t)BuIN)Te(mu-N(t))Bu)(2)Te(mu-O)](2)(I(3))(2) (3), [((t)BuMeN)Te(mu-N(t)Bu)(2)Te(mu-O)](2)(I(3))(2) (6), and 6.2MeCN, are also reported.

Journal Article↗
PubMed2005

A stable N-heterocyclic carbene with a diboron backbone.

The synthesis of a novel five-membered inorganic ring, a stable N-heterocyclic carbene with a diboron backbone, is reported. A pentacarbonyltungsten complex containing the new carbene is also described. Spectroscopic evidence indicates that the sterically encumbered carbene is a better sigma-donor than classical N-heterocyclic analogues, demonstrating the significant influence of the inorganic backbone on the coordinating properties of the carbon ligand. Crystal structures have been determined for an iminium precursor, the free carbene, and the tungsten complex.

Journal Article↗
PubMed2005

Preparation and crystal structure of two bicyclo[1.1.0]butan-2-ones: a hybrid oxyallyl-cyclopropanone motif.

The first X-ray crystal structures of two different bicyclo[1.1.0]butanones show a very long transannular bond of 1.69 A and a large carbonyl pyramidal distortion of 0.26 A out of the plane of the three carbons. These features are those expected of molecules with a hybrid cyclopropanone-oxyallyl structure, and these structures differ markedly from those of the parent bicyclo[1.1.0]butane skeleton.

Journal Article↗
PubMed2005

Microbial transformation of (-)-isolongifolol and butyrylcholinesterase inhibitory activity of transformed products.

The microbial transformation of (-)-isolongifolol (1) by using the standard two-stage fermentation technique with Fusarium lini afforded polar oxygenated metabolites: 10-oxoisolongifolol (2), 10alpha-hydroxyisolongifolol (3), and 9alpha-hydroxyisolongifolol (4). Metabolites 3 and 4 were also formed with the incubation of 1 with Aspergillus niger. All three metabolites were found to be new. Compounds 3 and 4 inhibited butyrylcholinesterase enzyme in a concentration-dependent manner with IC50 values 13.6 and 299.5 microM, respectively. Compound 3 showed un-competitive mode of inhibition against butyrylcholinesterase with Ki value 15.0 microM. The structures of metabolites 2-4 were deduced on the basis of spectroscopic techniques and single-crystal X-ray diffraction techniques.

Aspergillus niger↗
PubMed2005

Insertion of acrylonitrile into palladium methyl bonds in neutral and anionic Pd(II) complexes.

The reactions of a series of Pd(II) methyl compounds of general formula LPd(NCCH(3))CH(3), where L is a bulky phenoxydiazene or phenoxyaldimine ligand with the polar olefin acrylonitrile (AN), are reported. The compounds react with an excess of AN to give the products of 2,1 insertion into the Pd-Me bond, yielding dimers and/or trimers which feature bridging alpha-cyano groups. The reactions were studied by low temperature (1)H NMR spectroscopy, revealing an initial formation of compounds featuring N-bound AN, which isomerized to an (unobserved) pi-bound species that rapidly underwent 2,1 insertion into the Pd-Me bond. Intermediate oligomeric complexes retaining a Pd-Me function were observed at low [AN] in these reactions. Under pseudo first-order conditions, k(obs) values of 8.5 x 10(-5) to 2.68 x 10(-3) M(-1) (-22 degrees C to 10 degrees C, 100 equiv of AN) and activation parameters of DeltaH++ = 14.4(5) kcal mol(-1) and DeltaS++ = -19(5) eu were obtained in one case. Comparison of the overall rates of insertion between two LPd(NCCH(3))CH(3), differing in the overall charge on the supporting ligand L, showed that the complex bearing a negatively charged ligand reacts with AN twice as fast as one with no anionic charge. The rates of insertion in both of these complexes are significantly faster than reported rates for analogous reactions in cationic Pd(II) derivatives, indicating that increasing the negative charge on the complex enhances the rate of AN insertion. These results provide fundamental mechanistic insights into a crucial reaction for incorporation of polar comonomers into alpha olefins via a coordination polymerization mechanism.

Journal Article↗
PubMed2005

Synthesis of the quinolizidine alkaloids (-)-lasubine II and (+/-)-myrtine by conjugate addition and intramolecular acylation of amino esters with acetylenic sulfones.

The conjugate additions of (2-piperidyl)acetate esters to acetylenic sulfones, followed by LDA-promoted intramolecular acylations, afforded cyclic enaminones that were readily converted into the corresponding 4-substituted 2-keto- or 2-hydroxyquinolizidines by stereoselective reduction and desulfonylation. This procedure was applied to the total synthesis of (-)-lasubine II from methyl (S)-(2-piperidyl)acetate and 2-(3,4-dimethoxyphenyl)-1-(p-toluenesulfonyl)ethyne. Similarly, methyl (+/-)-(2-piperidyl)acetate and 1-(p-toluenesulfonyl)propyne provided (+/-)-myrtine.

Journal Article↗
PubMed2005

Aqueous suspension polymerization of isobutene initiated by 1,2-C6F4[B(C6F5)2]2.

Lewis acidic, chelating diborane 1 forms stable oxonium acids 2 in the presence of excess MeOH or water. Diborane 1 is shown to be an effective co-initiator for the suspension polymerization of isobutene in aqueous media at sufficiently low temperatures. Poly(isobutene) or butyl rubber is obtained at moderate to high conversion and with Mw < 200 K and PDI approximately 2 under these conditions.

Journal Article↗
PubMed2005

New diterpene isopimara-7,15-dien-19-oic acid and its prolyl endopeptidase inhibitory activity.

The ethanolic extract of the bulbs of Fritillaria imperialis was subjected to fractionation by solvent-solvent extraction. The nonpolar fraction showed inhibitory activity against prolyl endopeptidase (PEP) (EC.3.4.21.26), a large intracellular enzyme that preferentially hydrolyze proline-containing oligopeptidase at the carboxylic side of a prolyl residue. We have isolated a diterpenoid isopimara-7,15-dien-19-oic acid (1) from the nonpolar fraction of F. imperialis, and on methylation of compound 1, a methylester 2 was obtained which is a known compound previously isolated from Fritillaria thunbergii. The present article describes the isolation and structural elucidation of isopimara-7,15-dien-19-oic acid (1) by single-crystal X-ray diffraction techniques along with its prolyl endopeptidase inhibitory activity.

Diterpenes↗
PubMed2004

An asymmetrically substituted borazine.

The B3N3 ring in the title compound, 1,3,5-tri-tert-butyl-2,4-difluoro-6-phenylcyclotriborazane, [PhF2B3N3(t)Bu3] or C18H32B3F2N3, an asymmetrically substituted borazine, is distorted from planarity. The molecule resides on a twofold axis. The N atoms of the N-B(Ph)-N group lie on opposite sides of the least-squares plane formed by the four remaining ring atoms, due to steric accommodation of the tert-butyl groups, a conformation not previously observed for a borazine. The B-N bond lengths are in the range 1.4283 (14)-1.4493 (12) A, due to the F substituents residing on two of the B atoms, which also produce a large deviation from 120 degrees in one of the B-N-B angles [ca 113.6 (1) degrees]. The phenyl group is twisted with respect to the B3N3 ring, the interplanar angle being 62.87 (5) degrees.

Journal Article↗
PubMed2004

3-Germyl-3,3-dimethylpropionic acid derivatives.

The crystal structures of 3,3-dimethyl-3-(trichlorogermyl)propionic acid, [Ge(C5H9O2)Cl3], 3,3-dimethyl-3-(triphenylgermyl)propionic acid, [Ge(C6H5)3(C5H9O2)], and 3,3-dimethyl-3-(tri-p-tolylgermyl)propionic acid, [Ge(C7H7)3(C5H9O2)], have slightly distorted tetrahedral geometries about the Ge atoms. All the structures form dimers via strong O-H...O hydrogen bonds, resulting in eight-membered rings that can be best described in terms of graph-set notation R2(2) (8).

Crystallography, X-Ray↗
PubMed2004

Catalytic transformations with copper-metalated diglycine conjugates.

A series of copper-metalated, water-soluble bis-diglycine conjugates were synthesized and characterized through spectroscopic methods. These conjugates were evaluated for the cleavage of phosphodiester substrates, supercoiled plasmid relaxation in the presence of co-oxidants, and for the oxidation of a diphenolic substrate, 2,6-dimethoxyphenol. Appreciable rate enhancements were observed for these reactions and the oxidative nucleolytic cleavage activity and phenol oxidative coupling was presumably manifested via formation of reactive oxygen species.

Catalytic Domain↗
PubMed2004

On the reaction of 1-oxa-4-thiaspiro[4.5]decan-7-one with PhLi. A reinvestigation.

Two diastereomeric alcohols are formed from the reaction of 1-oxa-4-thiaspiro[4.5]decan-7-one with PhLi as against the single diastereomer reported earlier. The diastereoselectivity achieved from PhMgBr is significantly higher than with PhLi. The use of Et(2)O/hexane = 2:1 as the solvent for the reaction with PhMgBr offered the highest (14:1) diastereocontrol.

Journal Article↗
PubMed2004

Novel sesterterpenes from Leucosceptrum canum of nepalese origin.

Two novel sesterterpenoids, leucosesterterpenone (1) and leucosesterlactone (2), with novel skeleta were isolated from the hexane extract of the medicinal plant, Leucosceptrum canum. Their structures were established by the analysis of NMR data and the single-crystal X-ray diffraction of compound 1. Compounds 1 and 2 were found to exhibit activity against prolylendopeptidase (PEP).

Lamiaceae↗
PubMed2004

Lithiation of (tBuNH)3PNSiMe3 and formation of tetraimidophosphate complexes containing M3O3 rings (M = Li, K): X-ray structure of the stable radical [(Me3SiN)P(mu3-N(t)Bu)3[mu3-Li(THF)]3(OtBu)).

The reaction of ((t)BuNH)(3)PNSiMe(3) (1) with 1 equiv of (n)BuLi results in the formation of Li[P(NH(t)Bu)(2)(N(t)Bu)(NSiMe(3))] (2); treatment of 2 with a second equivalent of (n)BuLi produces the dilithium salt Li(2)[P(NH(t)Bu)(N(t)Bu)(2)(NSiMe(3))] (3). Similarly, the reaction of 1 and (n)BuLi in a 1:3 stoichiometry produces the trilithiated species Li(3)[P(N(t)Bu)(3)(NSiMe(3))] (4). These three complexes represent imido analogues of dihydrogen phosphate [H(2)PO(4)](-), hydrogen phosphate [HPO(4)](2)(-), and orthophosphate [PO(4)](3)(-), respectively. Reaction of 4 with alkali metal alkoxides MOR (M = Li, R = SiMe(3); M = K, R = (t)Bu) generates the imido-alkoxy complexes [Li(3)[P(N(t)Bu)(3)(NSiMe(3))](MOR)(3)] (8, M = Li; 9, M = K). These compounds were characterized by multinuclear ((1)H, (7)Li, (13)C, and (31)P) NMR spectroscopy and, in the cases of 2, 8, and 9.3THF, by X-ray crystallography. In the solid state, 2 exists as a dimer with Li-N contacts serving to link the two Li[P(NH(t)Bu)(2)(N(t)Bu)(NSiMe(3))] units. The monomeric compounds 8 and 9.3THF consist of a rare M(3)O(3) ring coordinated to the (LiN)(3) unit of 4. The unexpected formation of the stable radical [(Me(3)SiN)P(mu(3)-N(t)Bu)(3)[mu(3)-Li(THF)](3)(O(t)Bu)] (10) is also reported. X-ray crystallography indicated that 10 has a distorted cubic structure consisting of the radical dianion [P(N(t)Bu)(3)(NSiMe(3))](.2)(-), two lithium cations, and a molecule of LiO(t)Bu in the solid state. In dilute THF solution, the cube is disrupted to give the radical monoanion [(Me(3)SiN)((t)BuN)P(mu-N(t)Bu)(2)Li(THF)(2)](.-), which was identified by EPR spectroscopy.

Journal Article↗
PubMed2004

Do the electronic effects of sulfur indeed control the pi-selectivity of gamma-sulfenyl Enones? An investigation.

The electronic effects of sulfur in gamma-sulfenyl enones are not transmitted to the carbonyl carbon through the pi bond as reported previously. The diastereoselectivity is rather controlled by a combination of several other factors. The steric effects arising from the substituents on the sulfur atom and the gamma-carbon and the bulk of the nucleophile constitute the major control elements.

Journal Article↗