Biomedical subjects

Loan K Vo

Publications and source records attributed to Loan K Vo.

3 recordsLinked to original sources

PubMed2004

Isotope effects and the nature of stereo- and regioselectivity in hydroaminations of vinylarenes catalyzed by palladium(ii)-diphosphine complexes.

[reaction: see text] The hydroamination of styrene with aniline catalyzed by phosphine-ligated palladium triflates exhibits a substantial (13)C isotope effect at the benzylic carbon. This supports rate-determining nucleophilic attack of amine on a eta(3)-phenethyl palladium complex. Deuterium exchange observations and predicted isotope effects based on DFT calculations support this mechanism. Selectivity in these reactions is determined by the facility of palladium displacement after reversible hydropalladation of the alkene.

Amines↗

PubMed2003

A few molecules can control the enantiomeric outcome. Evidence supporting absolute asymmetric synthesis using the Soai asymmetric autocatalysis.

[reaction: see text] Experiments were carried out to investigate whether the Soai asymmetric autocatalysis can accomplish true absolute asymmetric synthesis. In 54 reactions, R and S enantiomeric products were obtained 27 times each. Of 25 pairs of side-by-side identical reactions, 12 afforded opposite enantiomers. In a test of the mechanistic viability of a random-chance process, it was found that a very few molecules (approximately 60 000) were sufficient to control the enantiomeric outcome of these reactions. These observations appear most consistent with asymmetric synthesis originating from the chance enantiomeric excess in a racemate.

Catalysis↗

PubMed2002

Enantioselective synthesis without discrete optically active additives.

By an adaptation of the asymmetric autocatalysis reactions of Soai, it was found that small enantiomeric excesses may be amplified to an arbitrary extent. When this process was applied 48 times to reactions in the absence of discrete optically active additives, all ultimately afforded substantial optical activity in the product. However, observations strongly suggest that most (and likely all) of these reactions are not true examples of absolute asymmetric synthesis. Rather, the ultimate optical activity arises from optically active impurities. Trace amounts of optically active materials may dominate the outcome of reactions involving asymmetric autocatalysis, and in the presence of opposite chiral influences a single enantiomer tends to take over a reaction. The possible implications of these observations to the origin of biological homochirality are noted.

Aldehydes↗