Biomedical subjects

Jim-Min Fang

Publications and source records attributed to Jim-Min Fang.

29 records · Page 2Linked to original sources

PubMed2003

Direct conversion of aldehydes to amides, tetrazoles, and triazines in aqueous media by one-pot tandem reactions.

A variety of aldehydes reacted with iodine in ammonia water at room temperature to give the nitrile intermediates, which were trapped by addition of hydrogen peroxide, sodium azide, or dicyandiamide to produce their corresponding amides, tetrazoles, and 1,3,5-triazines in modest to high yields. The one-pot tandem reactions were conducted in water media, and the products were obtained simply by extraction or filtration.

Journal Article↗

PubMed2002

Stereoselective synthesis of Neu5Acalpha(2-->5)Neu5Gc: the building block of oligo/poly(-->5-O(g)(lycolyl)Neu5Gcalpha2-->) chains in sea urchin egg cell surface glycoprotein.

The synthesis of a sialic acid dimer derivative, Neu5Acalpha(2-->5)Neu5Gc, is described. The synthetic strategy is based on the use of allyl alcohol to achieve an exclusive alpha-sialylation product. The allyloxy group is also a latent glycolic acid that provides the subsequent coupling with neuraminate with minimal protection-deprotection manipulations.

Animals↗

PubMed2002

2,7-Bis(1H-pyrrol-2-yl)ethynyl-1,8-naphthyridine: an ultrasensitive fluorescent probe for glucopyranoside.

[structure: see text] A push-pull conjugated molecule, 2,7-bis(1H-pyrrol-2-yl)ethynyl-1,8-naphthyridine (BPN), has been designed to bind selectively with octyl glucopyranoside (OGU). The BPN/OGU quadruple hydrogen-bonding complex adopts a rigid BPN conformation in which the proton donor (d) and acceptor (a) relays (daad) are resonantly conjugated through the ethynyl bridge, inducing pi-electron delocalization, i.e., a charge transfer effect. The excellent photophysical properties make BPN a highly sensitive probe for monitoring glucopyranoside to a detection limit of approximately 100 pM.

Binding Sites↗

PubMed2002

Synthesis of polysubstituted benzothiophenes and sulfur-containing polycyclic aromatic compounds via samarium diiodide promoted three-component coupling reactions of thiophene-2-carboxylate.

By the promotion of samarium diiodide, thiophene-2-carboxylate reacted with 2 equiv of ketones at the C-4 and C-5 positions to give diols such as 2 and 9. Because the intermediary organosamarium species were oxophilic but not too basic, the double hydroxyalkylations with various ketone substrates, including alkyl aryl ketones, acetylthiophenes, cyclohexanone, alpha-tetralone, and alpha-phenylacetophenones, were realized without complication of side reactions. The diol products underwent an acid-catalyzed dehydration to give dienes such as 3 and 10, which were treated with DDQ to give either polysubstituted thiophenes (e.g., 4 and 11) or benzothiophenes (e.g., 5, 13, and 14) depending on the reaction conditions. Oxidative annulations of 4,5-diarylthiophenes 11 and 4,5,6,7-tetraphenylbenzothiophenes 14 were carried out by photochemical or chemical methods to give the sulfur-containing polycyclic aromatic compounds, such as phenanthro[9,10-b]thiophene-2-carboxylate, piceno[13,14-b]thiophene-2-carboxylate, and tribenzo[fg,ij,rst]pentapheno[15,16-b]thiophene-2-carboxylates. This method is applicable to the preparation of polysubstituted thiophenes, benzothiophenes, and the related compounds possessing liquid crystalline, photochromic, and other functional properties.

Journal Article↗

PubMed2002

A novel photochromic system of 4,5-dialkenylthiophenes constructed by the smarium diiodide promoted coupling reactions of thiophene-2-carboxylate with aryl ketones.

[reaction: see text] The SmI2-promoted coupling reaction of ethyl thiophene-2-carboxylate with aryl ketones (2 equiv), followed by acid-catalyzed dehydration and oxidative aromatization, gave dialkenylthiophenes 1b-d, which underwent electrocyclizations upon irradiation with 300-nm light in CH3CN solution to give the corresponding closed-ring species with absorption lambda(max) approximately 425 nm. The interconversion between dialkenylthiophenes and their corresponding closed-ring species constitutes a novel photochromic system bearing an ester group for potential uses in linkage and wavelength tuning.

Journal Article↗

PubMed2002

A novel phosphate chemosensor utilizing anion-induced fluorescence change.

[structure: see text] The neutral receptor N,N'-bis[3,5-di[(1-pyrenylmethyl)carbamoyl]benzyl] pyridine-2,6-dicarbamide (2) provides a pseudo-tetrahedron cleft and multiple hydrogen bondings to form a 1:1 complex with phosphate ion in a highly selective manner, by comparison with other anions (F(-), Cl(-), Br(-), SCN(-), AcO(-), NO(3)(-), ClO(4)(-), and HSO(4)(-)). The binding strength can be inferred from the emission intensity ratio of the pyrene monomer (lambda(max) 377 nm) to the excimer (lambda(max) 477 nm). Fluorescence titration, X-ray analysis, and NMR studies support a proposed complexation model.

Crystallography, X-Ray↗

PubMed1999

Pinane-Type Tridentate Reagents for Enantioselective Reactions: Reduction of Ketones and Addition of Diethylzinc to Aldehydes.

The reduction of aryl and alkenyl methyl ketones using lithium aluminum hydride modified with (1R,2S,3S,5R)-(+)-10-anilino-3-ethoxy-2-hydroxypinane (10b) afforded chiral secondary alcohols in 83-96% chemical yields and 50-91% ee with dominance of R enantiomers. The reduction of acetophenone in the presence of lithium iodide gave the alcohol product with higher ee. On the other hand, the addition reaction of diethylzinc to benzaldehyde using the pinane-based diols 5-9 as promoters gave 1-phenylpropanol in favor of the S enantiomer up to 88% ee. Using the pinane-based alcohols 10a-e as promoters, the R enantiomer was obtained as the major product. The addition reactions of diethylzinc to various substituted benzaldehydes, employing the diol ligands 5c and 8e, afforded predominantly the corresponding (S)-alcohols. The chiral modifiers 5-10 were prepared from (1R)-(-)-myrtenol and were readily recovered (>90%) after the asymmetric reactions. In this study, LAH reduction and Et(2)Zn addition are complementary methods for the preparation of optically active secondary alcohols. The ligand 10-butylanilino-2,3-dihydroxypinane 5c promoted the Et(2)Zn additions effectively, whereas the modifier 10-anilino-3-ethoxy-2-hydroxypinane 10binduced the LAH reductions in a highly enantioselective manner.

Journal Article↗

PubMed1999

Samarium Ion-Promoted Cross-Aldol Reactions and Tandem Aldol/Evans-Tishchenko Reactions.

Cross-aldol reactions of carbonyl compounds were achieved by the catalysis of SmI(2) or SmI(3), together with molecular sieves, at ambient temperature. 1,3-Dichloroacetone and 1-chloroacetone can be used as acceptor substrates in the cross-aldol reactions with donor substrates such as acetone, cyclopentanone, and cyclohexanone. The cross-aldol reactions with (R)-glyceraldehyde acetonide gave optically pure compounds 25-32, the stereochemistry of which was in agreement with a chairlike chelate transition state of dipolar mode. SmI(2)-molecular sieves or SmI(3)-molecular sieves also functioned as effective Lewis acids to catalyze tandem aldol/Evans-Tishchenko reactions. The aldol/Evans-Tishchenko reactions of methyl ketones with aldehydes occurred at 0 degrees C to give alpha,gamma-anti diol monoesters 53a-59a. When the reactions were conducted at room temperature, a certain degree of transesterification took place. The aldol/Evans-Tishchenko reactions of ethyl or benzyl ketones with aldehydes yielded alpha,beta-anti-alpha,gamma-anti diol monoesters 60a-65a. However, the aldol/Evans-Tishchenko reactions of cyclic ketones with benzaldehyde occurred with a different stereoselectivity to give alpha,beta-syn-alpha,gamma-anti diol monoesters 66a-76a. The structures of products were determined by chemical and spectroscopic methods including an X-ray diffraction analysis of 72a derived from the reaction of 4-tert-butylcyclohexanone and benzaldehyde. A reaction mechanism involving dissociation-recombination of aldols followed by intramolecular stereoselective hydride shift is proposed, based on some experimental evidence, to explain the dichotomous stereoselectivity using acyclic or cyclic ketones as the reaction substrates.

Journal Article↗

PubMed1997

Preparation of Optically Active Tertiary Alcohols by Enzymatic Methods. Application to the Synthesis of Drugs and Natural Products.

By the catalysis of AK or porcine pancreas lipases, 3-iodo-2-phenyl-1,2-propanediol, 1-(hydroxymethyl)-1-phenyloxirane, 2-(iodomethyl)-4-phenyl-3-butyne-1,2-diol, 2-(iodomethyl)-4-(trimethylsilyl)-3-butyne-1,2-diol, and 5,5-dimethyl-2-(iodomethyl)-3-hexyne-1,2-diol were resolved in very high enantioselectivities (E >/= 153). The obtained enantiomerically pure or optically enriched compounds, containing an iodo atom, an oxirane moiety, or an alkynyl group, are versatile building blocks for the synthesis of chiral azido diols, sulfanyl diols, cyano diols, the side chain of a vitamin D(3) metabolite, the omega-chain of a prostaglandin analog, and an aggregation pheromone (1S,5R)-(-)-frontalin. Models based on the consideration of the importance of size, distance, and electron effect are proposed to interpret the observed stereospecificity in the enzymatic reactions. Thus, the lipase-catalyzed reactions of 1,1-disubstituted 1,2-diols occurred efficiently at the primary hydroxyl groups while the enantioselectivity was controlled by the tertiary carbinyl centers.

Journal Article↗

PubMed1996

Reductions, Reductive Alkylations, and Intramolecular Cyclizations of Acyl Silanes with Samarium Diiodide or Tributyltin Hydride.

A series of acyl silanes including aliphatic-, aromatic-, and bis-acyl silanes, as well as the acyl silanes bearing other substituents such as a bromine atom and alkenyl, succinimide, and carbonyl groups, were prepared, and their reactions with samarium diiodide or tributylstannane were studied. The reactions of acyl silanes occurred in various manners such as reductions, reductive alkylations, intramolecular radical cyclizations, pinacol couplings, aldol reactions, and Tishchenko reactions, depending on the nature of substrates and reaction conditions. Acyl silanes were generally reduced to give the corresponding alpha-silyl alcohols without transfer of silyl groups. Intramolecular radical cyclizations of 5-hexenoyl silanes and 1-silyl-1,5-pentanedione were realized to give alpha-silyl cyclopentanols and 1,2-cyclopentanediol derivatives, respectively. On treatment with samarium diiodide in tetrahydrofuran, 1-(trimethylsilyl)-1,6-hexanedione underwent a pinacol coupling reaction in the presence of t-BuOH, whereas it underwent a Tishchenko reaction in the presence of MeOH. The Tishchenko reaction of 1-silyl-1,5-pentanedione gave a delta-silyl-delta-lactone. On treating with samarium diiodide, 1-(trimethylsilyl)-1,5-hexanedione and 1,5-bis(trimethylsilyl)-1,6-hexanedione, underwent, respectively, intramolecular aldol reactions.

Journal Article↗

PubMedDate not supplied

Liquid-phase combinatorial synthesis of 1,4-benzodiazepine-2,5-diones as the candidates of endothelin receptor antagonism.

A library of 1,4-benzodiazepine-2,5-dione dicarboxylate derivatives containing aryl substituents at N(1)- and N(4)-positions to mimic the amino acid residues of Try-13, Phe-14, and Asp-18 in endothelin-1 is established by using the starting materials of alpha-amino esters, hydroxybenzaldehydes, nitrobenzoyl chlorides, and benzyl bromides in a polyethylene resin-bound liquid-phase synthesis. All of the six synthetic steps are conducted under mild conditions to give the desired products with reasonable yields and purity. The poly(ethylene glycol) support plays as a part of ester linkage that is released at the final step.

Benzodiazepinones↗