Phenyl versus ethyl transfer in the addition of organozinc reagents to aldehydes: a theoretical study.
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Biomedical subjects
Torben Rasmussen
Publications and source records attributed to Torben Rasmussen.
Modeling the stereoselectivity of the beta-amino alcohol-promoted addition of dialkylzinc to aldehydes.
The title reaction has been modeled by a Q2MM force field, allowing for rapid evaluation of several thousand TS conformations. For 10 experimental systems taken from the literature, the pathway leading to the major enantiomer has been identified. Furthermore, several possible contributions to the minor enantiomer have been investigated, providing an identification of the reasons for the sometimes moderate enantioselectivity of the title reaction, and allowing for future rational improvement of existing ligands. The favored pathways to the minor enantiomer, which must be blocked for significant selectivity improvement, differ strongly among ligands. Thus, design ideas are not necessarily transferable between ligand classes, but must be developed for each reaction on the basis of the pathway that needs to be blocked in each specific case. However, we have identified some general structure-selectivity relationships.
Journal Article↗
On the mechanism of the copper-catalyzed cyclopropanation reaction.
The selectivity-determining step in enantioselective copper-catalyzed cyclopropanation with diazo compounds has been studied by experimental and computational methods. The addition of the very reactive metallacarbene intermediate in an early transition state to the substrate alkene is concerted but strongly asynchronous, with substantial cationic character on one alkene carbon in the neighborhood of the transition state. Evidence from isotope effects and Hammett studies supports the nature of the transition state. Formation of a metallacyclobutane intermediate by a [2+2] addition is kinetically disfavored. Ligand-substrate interactions influencing the enantio- and diastereoselectivity have been identified, and the preferred orientation of the alkene substrate during the addition is suggested.
Journal Article↗
Postoperative changes on pulmonary function after laparoscopic and open cholecystectomy.
BACKGROUND/AIMS: We examined 28 patients who underwent cholecystectomy for acute or chronic cholecystitis and/or cholelithiasis in order to evaluate the effect of surgical technique on respiratory functional parameters. METHODOLOGY: We compared lung volume, flow parameters and blood gas indices in two groups of patients, eighteen of which underwent laparoscopic and ten of which open cholecystectomy, specifically on the 2nd and 8th postoperative day lung function indices were compared to preoperative values. The same anesthetic protocol was administered for all patients. No underlying illness other than the cholecystitis and/or cholelithiasis was present. RESULTS: From the results of lung volume parameters, ERV (%pred) data indicate a better expiratory ability for the Open Cholecystectomy [preop.: 93.10 (38.80), 8th day: 116.90 (63.69) compared to the Laparoscopic Cholecystectomy group (preop.: 105.39 (31.51), 8th day: 98.72 (35.80). For IC (%pred.) parameter, in the Open Cholecystectomy group a marked but not statistically significant decrease remained into the 8th day (preop.: 86.70 (16.40). 8th day: 68.40 (16.98)] whereas for the Laparoscopic Cholecystectomy group, IC %pred value reflected a better respiratory performance [preop.: 92.83 (17.87), 8th day: 82.50 (18.82)]. For RV and RV/TLC parameter measurements a marked increase in the %pred value was observed for the Laparoscopic Cholecystectomy group on the 8th postoperative day as compared to preoperative data [RV: 122.94 (42.80), 109.22 (33.23) respectively, RV/TLC: 122.68 (31.10), 109.14 (21.56) respectively]. From the analysis of the flow parameters, a distinct difference was evident for PEF between the preoperative and 8th postoperative day data with the Laparoscopic Cholecystectomy group showing statistically significant better flow rates [preop.: 93.72 (15.91), 8th day: 84.33 (20.67)] as compared to the Open Cholecystectomy group [preop.: 82.30 (22.98), 8th day: 59.10 (15.23)]. CONCLUSIONS: Having compared the 8th postoperative day with preoperative data for the two surgical methods, open cholecystectomy presented a better expiratory performance as compared to the laparoscopic method. However, laparoscopic cholecystectomy resulted in an overall better postoperative respiratory function.
Adult↗