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Six-membered Heterocyclic Ring (six-membered + heterocyclic_ring)

Distribution by Scientific Domains
Chemistry100%

Selected Abstracts

Conformational exchange in pimonidazole,a hypoxia marker

MAGNETIC RESONANCE IN CHEMISTRY, Issue 8 2007
Cristina Gabellieri
Abstract Pimonidazole is one of a series of nitroimidazole compounds that is widely used as a marker for qualitative and quantitative assessment of tumour hypoxia. We have observed a novel dynamic conformational exchange process in this molecule in aqueous solution. By a combination of 1H, 13C, two-dimensional 1H,1H EXchange SpectroscopY (EXSY) and spectral simulation, we unambiguously attribute the conformational exchange process to flipping of the six-membered heterocyclic ring. Copyright © 2007 John Wiley & Sons, Ltd. [source]

Influence of substituent groups at the 3-position on the mass spectral fragmentation pathways of cephalosporins

RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 14 2010
Jin Li
The structural fragment ions of nine cephalosporins were studied by electrospray ionization quadrapole trap mass spectrometry (Q-Trap MSn) in positive mode. The influence of substituent groups in the 3-position on fragmentation pathway B, an ,-cleavage between the C7C8 single bond, coupled with a [2,4]-trans-Diels-Alder cleavage simultaneously within the six-membered heterocyclic ring, was also investigated. It was found that when the substituent groups were methyl, chloride, vinyl, or propenyl, fragmentations belonging to pathway B were detected; however, when the substituents were heteroatoms such as O, N, or S, pathway B fragmentation was not detected. This suggested that the [M,R3]+ ion, which was produced by the bond cleavage within the substituent group at the 3-position, had a key influence on fragmentation pathway B. This could be attributed to the strong electronegativity of the heteroatoms (O, N, S) that favors the production of the [M,R3]+ ion. Moreover, having the positive charge of the [M,R3]+ ion localized on the nitrogen atom in the 1-position changed the electron density distribution of the heterocyclic structure, which prohibits a [2,4]-reverse-Diels-Alder fragmentation and as a result fragmentation pathway B could not occur. The influence of the substituent group in the 3-position was determined by the intensity ratio (e/d) of ions produced by fragmentation pathway A, a [2,2]-trans-Diels-Alder cleavage within the quaternary lactam ring, including the breaking of the amide bond and the C6C7 single bond (ion d), and fragmentation pathway B (ion e). The results indicate that the electronegativity of the substituent group was a key influencing factor of pathway B fragmentation intensity, because the intensity ratio (e/d) is higher for a chlorine atom, a vinyl, or a propenyl group than that of a methyl group. This study provided some theoretical basis for the identification of cephalosporin antibiotics and structural analysis of related substances in drugs. Copyright © 2010 John Wiley & Sons, Ltd. [source]

Conformational and configurational disorder in 6-(3,4,5-trimethoxyphenyl)-6,7-dihydro-5H -1,3-dioxolo[4,5- g]quinolin-8(5H)-one and 6-(1,3-benzodioxol-5-yl)-6,7-dihydro-5H -1,3-dioxolo[4,5- g]quinolin-8-one: a hydrogen-bonded chain of rings and ,-stacked hydrogen-bonded chains

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 7 2009
Paola Cuervo
In 6-(3,4,5-trimethoxyphenyl)-6,7-dihydro-5H -1,3-dioxolo[4,5- g]quinolin-8(5H)-one, C19H19NO6, (I), the six-membered heterocyclic ring adopts a conformation intermediate between envelope and half-chair forms; it is disordered over two enantiomeric configurations, with occupancies of 0.879,(3) and 0.121,(3), leading to positional disorder of the 3,4,5-trimethoxyphenyl unit. In 6-(1,3-benzodioxol-5-yl)-6,7-dihydro-5H -1,3-dioxolo[4,5- g]quinolin-8-one, C17H13NO5, (II), the molecules are similarly disordered, with occupancies of 0.866,(4) and 0.134,(4). The molecules in (I) are linked by one three-centre N,H...(O)2 hydrogen bond and one two-centre C,H...O hydrogen bond to form a complex chain of rings whose formation is reinforced by two independent aromatic ,,, stacking interactions. In (II), a single N,H...O hydrogen bond links the molecules into a simple chain, and pairs of chains are linked by a single aromatic ,,, stacking interaction. [source]

18-De­oxy-13,,14-dihydrolycoctam: the lycoctamone rearrangement confirmed

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 5 2006
Michael Benn
The structure of the title compound, C23H35NO4, contains a unique penta­cyclic ring system wherein one cyclo­hexyl ring adopts a chair conformation, two cyclo­hexyl rings are in boat conformations, and a six-membered heterocyclic ring and a cyclo­pentyl ring are in envelope conformations. The structures of the lycoctamones, ,,,-unsaturated aldehydes produced by acid-catalyzed degradation of lactams of lycoctonine-type alkaloids, previously deduced from the results of extensive chemical investigations have been proven to be correct by the determination of the crystal structure of this compound. [source]

3,,4,-Bis(4-chloro­phenyl)­spiro­[chroman-3,5,(4,H)-isoxazol]-4-one

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 4 2001
A. Abdul Ajees
The title compound, C23H15Cl2NO3, crystallizes with two independent mol­ecules in the asymmetric unit. The chroman­one moiety consists of a benzene ring fused with a six-membered heterocyclic ring which adopts a sofa conformation. The five-membered spiro­isoxazoline ring is in an envelope conformation. The p -chloro­phenyl rings bridged by the five-membered ring are nearly perpendicular to each other. The chromanone moiety of one mol­ecule packs into the cavity formed by the p -chloro­phenyl rings of a second mol­ecule through the formation of C,H,, interactions. The structure is stabilized by weak C,H,O, C,H,Cl and C,H,, interactions. [source]