Using molecular mechanics method,values of the heat of formation (HF) of different conformations,of perylenequinonoid photosensitizes hypocrellin A (HA) and hypocrellin B (HB) were calculated and the variance of HF af...Using molecular mechanics method,values of the heat of formation (HF) of different conformations,of perylenequinonoid photosensitizes hypocrellin A (HA) and hypocrellin B (HB) were calculated and the variance of HF after phenolic protons' dissociation were calculated as well The following was found:(i) The HF values of lour conformational isomers of HA and HB are similar to each other,so the four isomcrs can transform to each other room temperature,(ii) There exists the difference between the ability of dissociation of phenolic protons of HA and that of HB,the former is higher than the latter (iii) There exist two intramolecular hydrogen bonds in HA and HB The bond energy is approximately 8 kJ/mol and the energy of conformation Ⅰ is lower than that of conformationⅡ The bond energy of HA is lower than that of HB.(iv) There exists a low energy snot when phenolic hydroxyl bond twists 180° from the position where hydrogen bond is formed,which suggests that this kind of conformation probably exists,(v) The phenolic hydrogen of HBMC forms hydrogen bond with the neighbouring nitrogen,which is its striticture basis of possessing photosensitizing activity.展开更多
A series of N-(naphthalen-1-yl)-N-(phenyl(quinolin-3-yl)methyl)amide derivatives were designed and synthesized as anti-Mycobacterium tuberculosis drugs. NMR spectra showed that two conformational isomers of these comp...A series of N-(naphthalen-1-yl)-N-(phenyl(quinolin-3-yl)methyl)amide derivatives were designed and synthesized as anti-Mycobacterium tuberculosis drugs. NMR spectra showed that two conformational isomers of these compounds exist in solution,which is not due to cis-trans isomerization of amide bond. We proposed that the spatial interactions between three large aromatic groups caused the conformational isomerization,which was supported by molecular modeling and X-ray diffraction.展开更多
The fatty acid derivatives, prepared from renewable natural oils, can be used as highly promising and potential substitutes for petrochemicals. The study of process improvement and stereochemical mechanism for prepari...The fatty acid derivatives, prepared from renewable natural oils, can be used as highly promising and potential substitutes for petrochemicals. The study of process improvement and stereochemical mechanism for preparing these derivatives would be beneficial for their industrial production. Conjugated linoleic acid (CLA) containing 9<em>cis</em>-11<em>trans</em> (9<em>c</em>, 11<em>t</em>) and 10<em>trans</em>-12<em>cis</em> (10<em>t</em>, 12<em>c</em>) isomers was prepared from <em>Salicornia herbacea</em> seed oil. Maleic anhydride cycloadduct of CLA (MAC) was prepared by an improved process, and it was characterized by FTIR, <sup>1</sup>H and <sup>13</sup>C NMR, <em>etc</em>. A new method to calculate conformers-ratio of CLA or MAC was also developed. Furthermore, the stereochemical mechanism for the improved preparation of MAC was proposed primarily by the calculation method above. The following observations were made: 1) The yield of MAC could reach as high as 96.7% under mild reaction conditions and with an easy and efficient product separation;2) The <em>trans-trans</em> CLA in the<em> s-cis</em> conformation acted as a predominant reactant to <em>Diels-Alder</em> [4 + 2] cycloaddition of maleic anhydride, which was the main reaction occurred simultaneously with catalytic configurational isomerizations of CLA in one step;3) From all studied CLA conformers, the most stable conformation was the s-trans conformation of trans-trans CLA, while the <em>s-cis</em> conformation of <em>trans-trans</em> CLA had the most favorable structural parameters for cyclohexenyl ring formation;4) Four MAC conformers derived from 9<em>c</em>, 11<em>t</em>- and 10<em>t</em>, 12c-CLA, were obtained as final main products that were determined to be <em>cis</em>-cycloadducts;5) The <em>endo/exo</em> ratios of the <em>cis</em>- cycloadducts derived from 9<em>c</em>, 11<em>t</em>- and 10<em>t</em>, 12<em>c</em>-CLA, were 2.14:1 and 1.99:1, respectively;and 6) The results obtained from the calculation method above were in excellent acc展开更多
基金Project supported by the National Natural Science Foundation of China
文摘Using molecular mechanics method,values of the heat of formation (HF) of different conformations,of perylenequinonoid photosensitizes hypocrellin A (HA) and hypocrellin B (HB) were calculated and the variance of HF after phenolic protons' dissociation were calculated as well The following was found:(i) The HF values of lour conformational isomers of HA and HB are similar to each other,so the four isomcrs can transform to each other room temperature,(ii) There exists the difference between the ability of dissociation of phenolic protons of HA and that of HB,the former is higher than the latter (iii) There exist two intramolecular hydrogen bonds in HA and HB The bond energy is approximately 8 kJ/mol and the energy of conformation Ⅰ is lower than that of conformationⅡ The bond energy of HA is lower than that of HB.(iv) There exists a low energy snot when phenolic hydroxyl bond twists 180° from the position where hydrogen bond is formed,which suggests that this kind of conformation probably exists,(v) The phenolic hydrogen of HBMC forms hydrogen bond with the neighbouring nitrogen,which is its striticture basis of possessing photosensitizing activity.
文摘A series of N-(naphthalen-1-yl)-N-(phenyl(quinolin-3-yl)methyl)amide derivatives were designed and synthesized as anti-Mycobacterium tuberculosis drugs. NMR spectra showed that two conformational isomers of these compounds exist in solution,which is not due to cis-trans isomerization of amide bond. We proposed that the spatial interactions between three large aromatic groups caused the conformational isomerization,which was supported by molecular modeling and X-ray diffraction.
文摘The fatty acid derivatives, prepared from renewable natural oils, can be used as highly promising and potential substitutes for petrochemicals. The study of process improvement and stereochemical mechanism for preparing these derivatives would be beneficial for their industrial production. Conjugated linoleic acid (CLA) containing 9<em>cis</em>-11<em>trans</em> (9<em>c</em>, 11<em>t</em>) and 10<em>trans</em>-12<em>cis</em> (10<em>t</em>, 12<em>c</em>) isomers was prepared from <em>Salicornia herbacea</em> seed oil. Maleic anhydride cycloadduct of CLA (MAC) was prepared by an improved process, and it was characterized by FTIR, <sup>1</sup>H and <sup>13</sup>C NMR, <em>etc</em>. A new method to calculate conformers-ratio of CLA or MAC was also developed. Furthermore, the stereochemical mechanism for the improved preparation of MAC was proposed primarily by the calculation method above. The following observations were made: 1) The yield of MAC could reach as high as 96.7% under mild reaction conditions and with an easy and efficient product separation;2) The <em>trans-trans</em> CLA in the<em> s-cis</em> conformation acted as a predominant reactant to <em>Diels-Alder</em> [4 + 2] cycloaddition of maleic anhydride, which was the main reaction occurred simultaneously with catalytic configurational isomerizations of CLA in one step;3) From all studied CLA conformers, the most stable conformation was the s-trans conformation of trans-trans CLA, while the <em>s-cis</em> conformation of <em>trans-trans</em> CLA had the most favorable structural parameters for cyclohexenyl ring formation;4) Four MAC conformers derived from 9<em>c</em>, 11<em>t</em>- and 10<em>t</em>, 12c-CLA, were obtained as final main products that were determined to be <em>cis</em>-cycloadducts;5) The <em>endo/exo</em> ratios of the <em>cis</em>- cycloadducts derived from 9<em>c</em>, 11<em>t</em>- and 10<em>t</em>, 12<em>c</em>-CLA, were 2.14:1 and 1.99:1, respectively;and 6) The results obtained from the calculation method above were in excellent acc
