Biomedical subjects

Michael Y Chiang

Publications and source records attributed to Michael Y Chiang.

At least 19 recordsLinked to original sources

PubMed2006

Junceellolides J-L, 11,20-epoxybriaranes from the gorgonian coral Junceella fragilis.

Three new 11,20-epoxybriarane diterpenoids, junceellolides J-L (1-3), along with a known metabolite, 4, have been isolated from the gorgonian coral Junceella fragilis. The structures of these metabolites were elucidated using spectroscopic methods. The cyclohexane rings were found to exist in boat form in briaranes 1 and 4 and in chair form in 2 and 3. The structure of 1 was further confirmed by chemical conversion and single-crystal X-ray diffraction analysis. The relationship between (13)C NMR chemical shifts and the conformation of the cyclohexane ring in briaranes possessing an 11,20-epoxy group are described. The briaranes 2 and 4 showed mild inhibitory effects on human neutrophil elastase release.

Animals↗

PubMed2006

Crassolides A-F, cembranoids with a trans-fused lactone from the soft coral Sarcophyton crassocaule.

Six new polyoxygenated cembrane-based diterpenoids possessing a trans-fused alpha-methylene-gamma-lactone, crassocolides A-F (1-6), have been isolated along with the known compound 7 from the ethyl acetate extract of a Taiwanese soft coral, Sarcophyton crassocaule. The structures of 1-6 have been established by detailed spectroscopic analysis, including 2D NMR (1H-1H COSY, HMQC, HMBC, and NOESY) spectroscopy, while their absolute configurations were determined using a modified Mosher's method for 1. The structure of 5 was further proven by X-ray diffraction analysis. The full assignment of NMR data of 7 is reported herein for the first time. The cytotoxicity of crassocolides 1-4, 6, and 7 against a limited panel of cancer cells was also determined.

Animals↗

PubMed2005

Synthesis and mesomorphic behavior of a donor-acceptor-type hexaazatriphenylene.

[structure: see text] A new donor-acceptor, 1,4,5,8,9,12-hexaazatriphenylene HATCNOR(n), is described. The synthesis of HATCNOR1 and HATCNOR6 is achieved by the regioselective displacement of 1,4,5,8,9,12-hexaazatriphenylene hexacarbonitrile (HATCN) with an alkoxy group. The X-ray analysis revealed self-assembly of HATCNOR1 in the solid state. HATCNOR6 is the new difunctionalized hexaazatriphenylene discotic liquid crystal.

Journal Article↗

PubMed2005

Sinulochmodins A-C, three novel terpenoids from the soft coral Sinularia lochmodes.

An unprecedented C,C-linked dimeric norcembranoid (sinulochmodin A, 1), a novel isocembranoid (sinulochmodin B, 2), and a novel yonarane norditerpenoid (sinulochmodin C, 3) were isolated from the soft coral Sinularia lochmodes. The structures of these metabolites were elucidated by extensive spectroscopic analysis and on the basis of the absolute structures of two related norditerpenoids (4 and 5), which were determined for the first time by a modified Mosher method. A plausible pathway for the biosynthesis of 1 and 3-5 from 2 was postulated. [structure: see text]

Animals↗

PubMed2005

Kadsuphilactones A and B, two new triterpene dilactones from kadsuraphilippinensis.

[structure: see text]. Two novel triterpene dilactones, kadsuphilactones A (1) and B (2), were isolated from the Taiwanese medicinal plant Kadsura philippinensis. The structures of 1 and 2 were elucidated on the basis of extensive spectroscopic methods, including two-dimensional NMR techniques, and confirmed by X-ray crystallographic analysis. Kadsuphilactone B (2) exhibited in vitro anti-HBV activity with IC(50) values of 6 microg/mL by HBsAg enzyme immunoassay.

Antiviral Agents↗

PubMed2005

Bis[2,2'-(phenylphosphinediyl)dibenzenethiolato-kappa3S,P,S']germanium(IV).

Two tridentate phosphinethiolate ligands, [PhP(C6H4S-2)2]2-, coordinate to the Ge(IV) centre in a facial manner yielding the title compound, [Ge(C18H13PS2)2], which exhibits a pseudo-twofold symmetry with the two P-atom donors in a cis configuration. The Ge centre has a distorted octahedral environment. Two phenyl rings, one from each of the phosphinethiolate ligands, are parallel to one another, indicating pi-pi interactions. The molecules are linked by weak C-H...pi and C-H...S interactions.

Journal Article↗

PubMed2005

Polyoxygenated steroids from the gorgonian Isis hippuris.

Eleven new hippuristanols (1-4, 7-9, and 11-14), along with eight known metabolites (5, 6, 10, and 15-19), have been isolated from the gorgonian coral Isis hippuris. Single-crystal X-ray diffraction analyses supported the structure elucidation of known steroids 5 and 10. The absolute structures of hippuristanols were established by application of modified Mosher's method on 19. Compounds 14-19 have been found to exhibit significant cytotoxicity against several cancer cell lines.

Animals↗

PubMed2004

New regio- and stereoselective O-deacetylated and epoxy products of taxanes isolated from Taxus mairei.

Deacylation of a taxoid mixture isolated from the roots of Taxus mairei followed by chromatographic fractionation resulted in the isolation of three new taxoid derivatives, 2alpha,9alpha,10beta-triacetoxy-5alpha,14beta-dihydroxy-4(20),11(12)-taxadiene (1), 9alpha,10beta-diacetoxy-2alpha,5alpha,14beta-trihydroxy-4(20),11(12)-taxadiene (2), and 9alpha,10beta-diacetoxy-2alpha,5alpha,14beta-trihydroxy-4,20-epoxy,11(12)-taxene (3). Epoxidation of 2 afforded 9alpha,10beta-diacetoxy-2alpha,5alpha,14beta-trihydroxy-4,20:11,12-diepoxytaxane (6), while epoxidation of 4 yielded 9alpha,10beta-diacetoxy-5alpha,13alpha-dihydroxy-4,20-epoxy,11(12)-taxene (7) and 9alpha,10beta-diacetoxy-5alpha,13alpha-dihydroxy-4,20:11,12-diepoxytaxane (8). The structures were elucidated by detailed analysis of their NMR spectra. The structure and relative stereochemistry of 7 was confirmed by X-ray crystallography.

Crystallography, X-Ray↗

PubMed2003

(2,2'-Diamino-4,4'-bi-1,3-thiazole-kappa2N3,N3')(oxydiacetato-kappa3O,O',O")copper(II) monohydrate.

The title compound, [Cu(C(4)H(4)O(5))(C(6)H(6)N(4)S(2))].H(2)O, displays a square-pyramidal coordination geometry. The tridentate oxydiacetate dianion chelates the Cu(II) atom in the facial mode. The large difference [0.487 (4) A] between the longest Cu-O distance in the basal plane and that in the apical direction correlates with the small displacement of the Cu(II) atom [0.0576 (13) A] from the basal plane towards the apex of the square pyramid. The intermolecular hydrogen-bonding network results in a closely overlapped arrangement of the coordination basal plane and the thiazole ring of a neighboring molecule.

Journal Article↗

PubMed2003

A facile route to polysubstitutedN-benzyl pyroglutamates.

[reaction: see text] Base-induced coupling/cyclization reactions of alpha-sulfonylacetamide with various ethyl (Z)-2-bromo-2-propenoates have been carried out. The polysubstituted pyroglutamate carbon skeleton, with three contiguous asymmetric centers, was built up in one step. A ring-closure mechanism is proposed for the reactions.

Journal Article↗

PubMed2003

Benzaldehyde 2,4-dinitrophenylhydrazone.

Crystals of the title compound, C(13)H(10)N(4)O(4), were obtained from a condensation reaction of benzaldehyde and 2,4-dinitrophenylhydrazine. The molecule assumes an approximately planar E configuration. Within the dinitrophenyl moiety, the average distance for the aromatic C-C bonds close to the imino group [1.417 (3) A] is appreciably longer than the average distance for the other aromatic C-C bonds in the same phenyl ring [1.373 (3) A]. This increased distance may be a result of the overlap of the non-bonding orbital of the imino N atom with the pi orbitals of the arene. It is likely that pi-pi stacking exists in the crystal structure.

Journal Article↗

PubMed2002

catena-Poly[[tetraaquairon(II)]-mu-succinato-kappa2O:O'].

The title complex, ([Fe(C(4)H(4)O(4))(H(2)O)(4)])(n), is an infinite polymeric compound bridged by the succinate dianion. Two carboxylate groups coordinate in a monodentate manner to the Fe(II) atom, in a trans fashion, with an O-Fe-O bond angle of 175.72 (6) degrees and Fe-O distances of 2.0886 (14) and 2.1008 (15) A. One of the uncoordinated carboxylate O atom forms an intramolecular hydrogen bond with a coordinated water molecule. Extensive hydrogen bonding between parallel polymeric complex chains results in a three-dimensional supramolecular structure.

Journal Article↗

PubMed2002

The effect of substituents on the phenyl portion of the imido ligand on the structure and properties of molybdenum(VI) imido complexes.

Anilines with alkyl substituents on the phenyl ring (ArNH2 = 2,4,6-trimethylaniline; 2,3-, 2,4-, 2,6-, and 3,4-dimethylaniline; and 2,6-diisopropylaniline) react with MoO(X)2(dtc)2 (X = Cl or Br; dtc = diethyldithiocarbamate) in methanol in the presence of 2 equiv of triethylamine to form ionic imido complexes of the type [MoNAr(dtc)3]2[Mo6O19] or MoNAr(dtc)3]4[Mo8O26]. The same reaction in THF with butyllithium as base yields imido complexes of the type MoNAr(X)2(dtc)2. The structures of three ionic, five chloro, and two bromo complexes have been determined by X-ray crystallography. In all complexes, the molybenum center is a distorted pentagonal bipyramid. While the structures are similar, the angles of the imido linkages differ. The effect of the substituents on the phenyl ring of the imido ligand on the 95Mo NMR chemical shifts was determined. The Mo nucleus becomes more deshielded with the substituents in the following order: 3,4-Me2 < 2,3-Me2 < 2,4-Me2 < 2,6-Me2 < 2,4,6-Me3 < 2,6 isopropyl. Complexes with more deshielded 95Mo centers tend to have angles of the imido linkage that are closer to 180 degrees.

Journal Article↗

PubMed2002

(R)-mandelic acid (S)-alanine hemihydrate.

Crystals of the title complex, C(3)H(7)NO(2).C(8)H(8)O(3).0.5H(2)O, were obtained from an aqueous solution containing racemic mandelic acid and (S)-alanine. The unit cell includes two independent molecular complexes and one water molecule. The structure formed by (R)-mandelic acid and (S)-alanine in a 1:1 molar ratio shows the successful optical separation of racemic mandelic acid. Strong hydrogen bonding, with a rather short O...O separation of 2.494 (3) A, is observed between the carboxyl and carboxylate groups. A structural comparison suggests that the strong hydrogen bonding affects the neighbouring covalent bond.

Journal Article↗

PubMed2002

Chlorobis(thiourea-kappa S)copper(I) bis(4,5-diazafluoren-9-one) monohydrate.

The title compound, [CuCl(CH(4)N(2)S)(2)] x 2C(11)H(6)N(2)O x H(2)O, consists of molecules of a Cu(I)-thiourea complex, free 4,5-diazafluoren-9-one (dafone) and crystalline water. The planar complex molecule has trigonal coordination geometry around the Cu(I) atom. The dafone and water molecules, which are hydrogen bonded to the Cu(I) complex, are approximately coplanar with this complex. The crystal displays a sheet structure and pi-pi stacking is observed between neighbouring sheets.

Journal Article↗

PubMed2002

(1R,3S)-Camphoramic acid.

The title chiral compound, 3-aminocarbonyl-1,2,2-trimethylcyclopentane-1-carboxylic acid, C(10)H(17)NO(3), was prepared from (1R,3S)-camphoric acid. The five-membered ring adopts a conformation which is intermediate between a twist and an envelope. Elongations of the C-C bonds and contractions of the C-C-C bond angles are observed within the five-membered ring. A (1)H NMR spectrum was recorded to assist in distinguishing the amide group from the carboxyl group.

Journal Article↗

PubMed2002

Lanostanoids of Amentotaxus formosana.

Three lanostanoids, 3beta-methoxycycloartan-24(24(1))-ene (1), 3beta,23beta-dimethoxycycloartan-24(24(1))-ene (2), and 3beta,23beta-dimethoxy-5alpha-lanosta-24(24(1))-ene (3), were isolated from the leaves of Amentotaxus formosana. The structures of new compounds 2 and 3 were determined by NMR and MS studies, and the structure of 3 was further confirmed by X-ray crystallographic analysis.

Crystallography, X-Ray↗

PubMed2002

Juncenolide A, a new briarane from the Taiwanese Gorgonian Junceella juncea.

Fractionation of the acetone extract of Junceella juncea collected in Taiwan resulted in the isolation of a new briarane, designated juncenolide A (1). The structure of 1 was determined on the basis of 2D NMR techniques, including COSY, HSQC, HMBC, and NOESY experiments, and was also confirmed by X-ray crystallographic analysis.

Animals↗