THE STRUCTURE AND STEREOCHEMISTRY OF ATISINE

1964 ◽  
Vol 42 (1) ◽  
pp. 137-149 ◽  
Author(s):  
D. Dvornik ◽  
O. E. Edwards
Keyword(s):  
Long Range ◽  
Rigorous Proof ◽  
Polar Groups ◽  
Detailed Explanation ◽  
Exocyclic Methylene ◽  
Derivatives Of ◽  
Methylene Group ◽  
Absolute Stereochemistry ◽  
Basic Strength

A stereospecific hydration of the exocyclic methylene group of a derivative of the alkaloid atisine has been observed. The product was used to degrade the alkaloid to a tetracyclic phenol. This enabled rigorous proof of the structure and relative and absolute stereochemistry of atisine and related alkaloids. A detailed explanation of the abnormal basic strength and the isomerization of atisine is given. Long-range influence of polar groups on the basic strength of derivatives of the alkaloid is reported.

Efficient Preparation of Novel Exocyclic Methylene Derivatives of Qinghaosu (Artemisinin) as Potential Antimalarial Agents

1994 ◽  
Vol 4 (4) ◽  
pp. 279-285 ◽  
Author(s):  
Ranjan P. Srivastava ◽  
Robert D. Sindelar ◽  
James D. McChesney
Keyword(s):  
Antimalarial Agents ◽  
Exocyclic Methylene ◽  
Derivatives Of

scholarly journals Relation between Crystal Structures of Precursors and Final Products: Example of Vitamin D Intermediates

Molecules ◽  
2020 ◽  
Vol 25 (8) ◽  
pp. 1802
Author(s):  
Monika Wanat ◽  
Maura Malinska ◽  
Andrzej Kutner ◽  
Krzysztof Woźniak
Keyword(s):  
Vitamin D ◽  
Crystal Structures ◽  
Theoretical Calculations ◽  
Geometrical Parameters ◽  
Space Groups ◽  
Vitamin D Analogues ◽  
Vitamin D Analog ◽  
Exocyclic Methylene ◽  
Solid Form ◽  
Methylene Group

In this paper, we proved that the solid-state structure of vitamin D analog is well represented by the structures of its structural fragments. This is important in predicting the biological activity of vitamin D analogs that are not available in the solid form. The previously published crystal structure of advanced vitamin D intermediate provided additional insights into vitamin D properties. A similar analysis based on simple vitamin D intermediate analogues showed that precursors crystallized in the space groups typical for vitamins D; geometrical parameters were related to the corresponding parameters in the vitamin D analogues; and crystal structures of the basic intermediates and their final products contained similar intermolecular interactions, essential for the infinite hydrogen bond motif observed in the vitamin D analogues. The energy of these interactions is related as shown by theoretical calculations, that is, energy frameworks analysis. Moreover, analysis of the hydrogen bonds motifs revealed a relation between these motifs and the absolute configuration of basic intermediates as well as the space orientation of the exocyclic methylene group in the final structures.

Diyne Cyclization in Camphor Derivatives - Experimental and Theoretical Investigation

1996 ◽  
Vol 51 (11) ◽  
pp. 1655-1662 ◽  
Author(s):  
Gabriele Wagner ◽  
Christian Heiß ◽  
Uwe Verfiirth ◽  
Rudolf Herrmann
Keyword(s):  
Oxygen Atom ◽  
Theoretical Investigation ◽  
Positive Charge ◽  
Membered Ring ◽  
Titanium Chloride ◽  
Nmr Studies ◽  
Methylene Carbon ◽  
Camphor Derivatives ◽  
Exocyclic Methylene ◽  
Derivatives Of

Derivatives of 3-oxo-camphorsulfonimide (1) with two phenylethynyl groups in the endo positions at the carbons C-2 and C-3 were prepared, and their reactivity towards halogenes and titanium chloride was studied. In every case, the two ethynyl groups led to the annulation of a five-membered ring to the bicyclo[2 .2 .1] system in an orientation which depends on the bulkiness of the additional substituent in position 3. NMR studies show that cationic species like 6 and 8 are the first detectable intermediates. They not only contain the fused five-membered ring but also a bond between its exocyclic methylene carbon and an oxygen atom of the sulfonyl group, thus transferring the positive charge mainly to sulfur. Semiempirical calculations (PM3) suggest two intermediates in the formation of such cations.

Attenuation of the Substituent Effects Along the Aliphatic Chain

2004 ◽  
Vol 69 (5) ◽  
pp. 984-995 ◽  
Author(s):  
Stanislav Böhm ◽  
Otto Exner
Keyword(s):  
Functional Group ◽  
Inductive Effect ◽  
Substituent Effects ◽  
Transmission Factor ◽  
Isodesmic Reaction ◽  
Aliphatic Chain ◽  
Model Compounds ◽  
Derivatives Of ◽  
Methylene Group ◽  
Isolated Molecules

Two series of model compounds were devised to follow the attenuation of substituent effects with an interposed methylene group: short-chain aliphatic compounds 1 and derivatives of bicyclo[2.2.2]octane 5. In all compounds, chlorine atom acts as substituent and charged oxygen atom as the functional group; the interaction of both is measured by the reaction energy of the isodesmic reaction calculated at the B3LYP/AUG-cc-pVTZ//B3LYP/6-311+G(d,p) and/or B3LYP/6-311+G(d,p) levels. Attenuation of the substituent inductive effect with the distance is less steep than observed previously in solution. It depends also markedly on the conformation but cannot be reproduced, not even approximately, by the electrostatic formula. Only for simple regular conformations, it can be described approximately by an exponential function with the transmission factor for one methylene group equal to 0.74. The behavior of isolated molecules differs in this case distinctly from the reactivity in solution. Nevertheless, the significance of the two formulas, electrostatic and exponential, is similar in the isolated molecules and in solution. These formulas represent only two different, rather crude mathematical approximations and cannot be given any physical meaning.

scholarly journals The cyclopropylcarbinyl route to γ-silyl carbocations

2019 ◽  
Vol 15 ◽  
pp. 1769-1780 ◽  
Author(s):  
Xavier Creary
Keyword(s):  
Long Range ◽  
Trimethylsilyl Group ◽  
Derivatives Of

The mesylate derivative of cis-1-hydroxymethyl-2-trimethylsilylcyclopropane has been prepared, along with a number of related mesylates and triflates with substituents on the 1-position. These substrates all solvolyze in CD3CO2D to give products derived from cyclopropylcarbinyl cations that undergo further rearrangement to give 3-trimethylsilylcyclobutyl cations. These 3-trimethylsilylcyclobutyl cations are stabilized by a long-range rear lobe interaction with the γ-trimethylsilyl group. When the substituent is electron-withdrawing (CF3, CN, or CO2CH3), significant amounts of bicyclobutane products are formed. The bicyclobutanes are a result of γ-trimethylsilyl elimination from the cationic intermediate that has an unusually long calculated Si–C bond. The solvolysis chemistry of mesylate and triflate derivatives of trans-1-hydroxymethyl-2-trimethylsilylcyclopropane and 1-substituted analogs can be quite different since these substrates do not generally lead to 3-trimethylsilylcyclobutyl cations.

scholarly journals Degradation of Benzo[a]pyrene by Mycobacterium vanbaalenii PYR-1

2004 ◽  
Vol 70 (1) ◽  
pp. 340-345 ◽  
Author(s):  
Joanna D. Moody ◽  
James P. Freeman ◽  
Peter P. Fu ◽  
Carl E. Cerniglia
Keyword(s):  
High Performance ◽  
Culture Media ◽  
Optical Purity ◽  
Fission Products ◽  
Reversed Phase ◽  
Environmental Pollutant ◽  
Ring Fission ◽  
Uv Visible ◽  
Derivatives Of ◽  
Absolute Stereochemistry

ABSTRACT Metabolism of the environmental pollutant benzo[a]pyrene in the bacterium Mycobacterium vanbaalenii PYR-1 was examined. This organism initially oxidized benzo[a]pyrene with dioxygenases and monooxygenases at C-4,5, C-9,10, and C-11,12. The metabolites were separated by reversed-phase high-performance liquid chromatography (HPLC) and characterized by UV-visible, mass, nuclear magnetic resonance, and circular dichroism spectral analyses. The major intermediates of benzo[a]pyrene metabolism that had accumulated in the culture media after 96 h of incubation were cis-4,5-dihydro-4,5-dihydroxybenzo[a]pyrene (benzo[a]pyrene cis-4,5-dihydrodiol), cis-11,12-dihydro-11,12-dihydroxybenzo[a]pyrene (benzo[a]pyrene cis-11,12-dihydrodiol), trans-11,12-dihydro-11,12-dihydroxybenzo[a]pyrene (benzo[a]pyrene trans-11,12-dihydrodiol), 10-oxabenzo[def]chrysen-9-one, and hydroxymethoxy and dimethoxy derivatives of benzo[a]pyrene. The ortho-ring fission products 4-formylchrysene-5-carboxylic acid and 4,5-chrysene-dicarboxylic acid and a monocarboxylated chrysene product were formed when replacement culture experiments were conducted with benzo[a]pyrene cis-4,5-dihydrodiol. Chiral stationary-phase HPLC analysis of the dihydrodiols indicated that benzo[a]pyrene cis-4,5-dihydrodiol had 30% 4S,5R and 70% 4R,5S absolute stereochemistry. Benzo[a]pyrene cis-11,12-dihydrodiol adopted an 11S,12R conformation with 100% optical purity. The enantiomeric composition of benzo[a]pyrene trans-11,12-dihydrodiol was an equal mixture of 11S,12S and 11R,12R molecules. The results of this study, in conjunction with those of previously reported studies, extend the pathways proposed for the bacterial metabolism of benzo[a]pyrene. Our study also provides evidence of the stereo- and regioselectivity of the oxygenases that catalyze the metabolism of benzo[a]pyrene in M. vanbaalenii PYR-1.

The proton magnetic resonance spectra of N-nitroso derivatives of sarcosine, proline and iminodiacetic acid

1971 ◽  
Vol 24 (9) ◽  
pp. 1949 ◽  
Author(s):  
FHC Stewart
Keyword(s):  
Magnetic Resonance ◽  
Long Range ◽  
Proton Magnetic Resonance ◽  
Iminodiacetic Acid ◽  
Conformational Isomerism ◽  
Nitroso Group ◽  
Restricted Rotation ◽  
Derivatives Of ◽  
Shielding Effects ◽  
Magnetic Resonance Spectra

The proton magnetic resonance spectra of various N-nitroso derivatives of sarcosine, L-proline, and iminodiacetic acid, including some protected dipeptides, have been obtained. Magnetic non-equivalence and conformational isomerism arising from restricted rotation of the nitroso group are discussed in relation to the reported behaviour of other nitrosamines. Long-range shielding effects on protons at a considerable distance from the anisotropic nitrosamino centre were readily detected with these compounds.

Investigation of the mobility of methylene group hydrogen atoms in some derivatives of 2-iminothiazolidin-4-one

1967 ◽  
Vol 3 (2) ◽  
pp. 516-518
Author(s):  
I. I. Chizhevskaya ◽  
R. S. Kharchenko ◽  
N. N. Khovratovich
Keyword(s):  
Hydrogen Atoms ◽  
Derivatives Of ◽  
Methylene Group
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