scholarly journals Structure and thermal interconversion of cyclobilirubin IX α

1984 ◽  
Vol 218 (3) ◽  
pp. 667-676 ◽  
Author(s):  
S Onishi ◽  
I Miura ◽  
K Isobe ◽  
S Itoh ◽  
T Ogino ◽  
...  
Keyword(s):  
Hydrogen Atom ◽  
Mass Spectra ◽  
Chemical Structure ◽  
Lactone Ring ◽  
Final Conclusion ◽  
Quaternary Carbon Atom ◽  
Methyl Group ◽  
Bilirubin Metabolism ◽  
To Come ◽  
Vinyl Group

One of the two main photoproducts in bilirubin metabolism during phototherapy in neonatal hyperbilirubinaemia is (EZ)-cyclobilirubin. However, it has not yet been possible to come to a final conclusion as to its chemical structure, despite the fact that much effort has been expended on the problem. The present paper demonstrates that (EZ)-cyclobilirubin is formed by the intramolecular cyclization of the C-3-vinyl group with the position at C-7 rather than at C-6, without delta-lactone-ring formation. The evidence comes from 13C-n.m.r. spectra, which indicate that an oxygen-bound quaternary carbon atom is not present, and from 1H-n.m.r. spectra, which indicate that the orientation of the methyl group at C-2 is equatorial; these findings are supported by mass spectra. The existence of both an epimeric relationship at C-7 between (EE)- and (EZ)-cyclobilirubins A and B and of steric isomers of the hydrogen atom and methyl group at C-2 is supported by the fact that the methyl-group protons at C-2 and C-7 are observed as a paired signal in 1H-n.m.r. spectra, and that new signals at C-7, C-2 and C-3 beta appear in 13C-n.m.r. spectra, that mass spectra of (EZ)-cyclobilirubins A and B are extremely similar and that, furthermore, thermal interconversion between (EE)- and (EZ)-cyclobilirubins A and B is observed.

scholarly journals Anaerobic and aerobic coproporphyrinogen III oxidases of Rhodopseudomonas spheroides. Mechanism and stereochemistry of vinyl group formation

1983 ◽  
Vol 209 (3) ◽  
pp. 709-718 ◽  
Author(s):  
J S Seehra ◽  
P M Jordan ◽  
M Akhtar
Keyword(s):  
Hydrogen Atom ◽  
Group Formation ◽  
Side Chains ◽  
Improved Method ◽  
Conversion Formula ◽  
Coproporphyrinogen Iii Oxidase ◽  
Rhodopseudomonas Spheroides ◽  
Vinyl Group

An improved method for the preparation of various species of porphobilinogen stereospecifically labelled with 3H in the side chains (at C-6, C-7 and C-8) is described. These labelled samples were used to study the mechanism and stereochemistry of anaerobic as well as aerobic coproporphyrinogen III oxidase of light-grown Rhodopseudomonas spheroides. It was shown that both the oxidases catalyse the conversion of the propionate side chains of coproporphyrinogen III into the vinyl groups of protoporphyrinogen IX, (formula; see text) with the labilization of the pro-S-hydrogen atom at the beta-position. These results are similar to those previously recorded for such conversions in animal and plant systems. In the light of the cumulative information available to date, mechanisms for the conversion, (formula; see text) are discussed and doubt is cast on the participation of hydroxylated intermediates in the process.

Chemical Ionization Mass Spectrometry of Organophosphorus Insecticides

1974 ◽  
Vol 57 (5) ◽  
pp. 1050-1055 ◽  
Author(s):  
Roy L Holmstead ◽  
John E Casida
Keyword(s):  
Mass Spectrometry ◽  
Electron Impact ◽  
Mass Spectra ◽  
Chemical Structure ◽  
Chemical Ionization ◽  
Ionization Mass Spectrometry ◽  
Chemical Ionization Mass Spectrometry ◽  
Ionization Mass ◽  
Organophosphorus Insecticides ◽  
Fragmentation Patterns

Abstract The chemical ionization (CI) mass spectra of 15 important organophosphorus insecticides and 14 of their major metabolites are discussed in relation to the effect of chemical structure on fragmentation patterns. The fragments obtained with CI are sometimes quite different from those formed on electron impact and, in general, simpler spectra are obtained with CI.

FURTHER DEGRADATION REACTIONS OF ANNOTININE

1955 ◽  
Vol 33 (5) ◽  
pp. 849-860 ◽  
Author(s):  
F. A. L. Anet ◽  
Léo Marion
Keyword(s):  
Amino Acid ◽  
Benzene Ring ◽  
Potassium Permanganate ◽  
Lactone Ring ◽  
Neutral Substance ◽  
Unsaturated Lactone ◽  
Degradation Reactions ◽  
Vinyl Group ◽  
Color Reactions ◽  
Chromous Chloride

Both the hydroxylactone obtained by the action of chromous chloride on annotinine chlorohydrin, and the unsaturated lactone B prepared by the action of the same reagent on the hydroxylactone, contain a secondary nitrogen and a vinyl group. The unsaturated lactone A which accompanies the hydroxylactone is a cyclic allylamine which on oxidation with potassium permanganate yields an amino acid C14H19O4N. These facts make it possible to explain the reaction of chromous chloride with annotinine chlorohydrin. The amino acid can be de-hydrogenated to an acid containing a free carboxyl and a lactamic grouping (C14H15O3N) but no longer containing a lactone ring. The lactamic acid which seems to contain a benzene ring is readily decarboxylated to a neutral substance C13H15ON, showing color reactions and ultraviolet absorption similar to those of strychnine.

Acid-catalyzed rearrangements of an A(1)-nor-triterpenoid 2α,3α-epoxide

1989 ◽  
Vol 54 (2) ◽  
pp. 413-429 ◽  
Author(s):  
Jiří Klinot ◽  
Jiří Liška ◽  
Alena Forgáčová ◽  
Miloš Buděšínský ◽  
Jiří Protiva ◽  
...  
Keyword(s):  
Acidic Medium ◽  
Boron Trifluoride ◽  
Mass Spectra ◽  
Boron Trifluoride Etherate ◽  
Methyl Group ◽  
Unsaturated Alcohols ◽  
Acid Catalyzed ◽  
C Nmr

Reactions of 2α,3α-epoxide X, derived from 19β,28-epoxy-A(1)-nor-18α-oleanane, with acids proceed with migration of the 10β-methyl group into the position 2β, giving rise to unsaturated alcohols XII and XIV and diene IX. Reaction with boron trifluoride etherate afforded ketone XI in addition to XII and XIV. Olefin VIII rearranged in acidic medium to give olefins XXVI and XXVII. The rearranged products were converted into other derivatives and their structure was established by 1H and 13C NMR, IR, UV and mass spectra.

Radiation and Radiationless Processes in 2,3-Pentanedione; Phosphorescence Lifetime in the Gas Phase

1971 ◽  
Vol 49 (7) ◽  
pp. 987-993 ◽  
Author(s):  
A. W. Jackson ◽  
A. J. Yarwood
Keyword(s):  
Hydrogen Atom ◽  
Triplet State ◽  
Gas Phase ◽  
Ground State ◽  
Hydrogen Atom Abstraction ◽  
Intersystem Crossing ◽  
Phosphorescence Lifetime ◽  
Gaseous State ◽  
Methyl Group ◽  
Intramolecular Hydrogen

Fluorescence and phosphorescence are observed when 2,3-pentanedione in the gaseous state is excited at 365, 405, and 436°nm. The phosphorescence lifetime has been investigated as a function of temperature (298 to 363 °K) and concentration of the diketone (0.5 to 90 × 10−4 M). A mechanism that explains the experimental data is proposed. Apart from the radiative process and an intersystem crossing to the ground state, the triplet state 2,3-pentanedione molecules are removed by two other processes. One is a unimolecular reaction with a rate constant of 1 × 1011 exp (−11.0/RT) s−1 (consistent with an intramolecular hydrogen atom abstraction), and the other is an interaction with ground state molecules. The photochemistry of the triplet state of 2,3-pentanedione is compared with that of biacetyl to consider the effect of substitution of a hydrogen atom by the methyl group on the radiationless processes in diketones.

An anomalous effect of methyl group on acidity of acylthioureas

1987 ◽  
Vol 52 (8) ◽  
pp. 1992-1998 ◽  
Author(s):  
Jaromír Kaválek ◽  
Josef Jirman ◽  
Vladimír Macháček ◽  
Vojeslav Štěrba
Keyword(s):  
Hydrogen Atom ◽  
Rate Constant ◽  
Rate Constants ◽  
Dissociation Constants ◽  
Acetyl Derivative ◽  
Methyl Groups ◽  
Anomalous Effect ◽  
Methyl Group ◽  
Methyl Derivatives

Dissociation constants and methanolysis rate constants have been measured of 1-acetyl- and 1-benzoylthioureas and their N-methyl derivatives. Replacement of hydrogen atom at N(1) (next to the acyl group) by methyl group increases the acidity of the benzoyl derivative by one order, that of the acetyl derivative by as much as two orders of magnitude. Replacement of both hydrogens at N(3) by methyl groups lowers the methanolysis rate constant by more than two orders, whereas the replacement of hydrogen atom at N(1) by methyl group increases the methanolysis rate by the factor of 30.

Kinetics of acid-catalyzed cyclization of substituted hydantoinamides to substituted hydantoins

1987 ◽  
Vol 52 (8) ◽  
pp. 1999-2004 ◽  
Author(s):  
Jaromír Kaválek ◽  
Vladimír Macháček ◽  
Gabriela Svobodová ◽  
Vojeslav Štěrba
Keyword(s):  
Hydrogen Atom ◽  
Nitrogen Atom ◽  
Hydrochloric Acid ◽  
Dissociation Constants ◽  
Amide Group ◽  
The Other ◽  
Methyl Group ◽  
Acid Catalyzed ◽  
Cyclization Rate ◽  
Kinetics Of

The kinetics of acid-catalyzed cyclization of the hydantoinamides type R3-N(5)H-CO-N(3)R2-CH2-CO-N(1)HR1 (R1, R2, R3 = H and/or CH3) has been studied in 0·5 to 5 mol l-1 hydrochloric acid. The cyclization rate is limited by the rate of the attack of nitrogen atom N(5) on the carbon atom of the protonated amide group. The dissociation constants of the protonated hydantoinamides and rate constants of their cyclizations have been determined. Replacement of hydrogen atom by methyl group at the N(5) nitrogen atom accelerates the cyclization about two times., the same substitution at N(3) accelerates about 50x, whereas at N(1) it results in a 300 fold retardation. With the hydantoinamides having R3 = CH3, the cyclization rate of the protonated hydantoinamide increases with increasing concentration of hydrochloric acid, whereas with the other derivatives this value is independent of the acid concentration.

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