- Enantioselectivity of haloalkane dehalogenases and its modulation by surface loop engineering
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In the loop: Engineering of the surface loop in haloalkane dehalogenases affects their enantiodiscrimination behavior. The temperature dependence of the enantioselectivity (lnE versus 1/T) of β-bromoalkanes by haloalkane dehalogenases is reversed (red data points) by deletion of the surface loop; the selectivity switches back when an additional single-point mutation is made. This behavior is not observed for -bromoesters.
- Prokop, Zbynek,Sato, Yukari,Brezovsky, Jan,Mozga, Tomas,Chaloupkova, Radka,Koudelakova, Tana,Jerabek, Petr,Stepankova, Veronika,Natsume, Ryo,Van Leeuwen, Jan G. E.,Janssen, Dick B.,Florian, Jan,Nagata, Yuji,Senda, Toshiya,Damborsky, Jiri
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supporting information; experimental part
p. 6111 - 6115
(2010/11/05)
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- Complete inversion of configuration in aliphatic nucleophilic substitution reactions with small inner-sphere stabilization
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The stereochemistry of the nucleophilic reaction of the enolate anion of 1,4-dihydro-4-methoxycarbonyl-1-methylpyridine (1-) with (R)-(-)- and (S)-(+)-2-bromobutane has been investigated and correlated with the inner-sphere stabilization of the reactions calculated from the ratio kSUB/kET, where kSUB is the rate of substitution and kET the expected rate of electron transfer. It was shown that 1- reacts with 2-bromobutane with nearly complete inversion of configuration (99.7%). A complete shift in stereochemistry of the nucleophilic reactions of 1- with alkyl halides from racemization to complete inversion is induced by a small increase in the inner-sphere stabilization of the transition state from 0 to 3 kcal mol-1. The results in this work suggest that the SN2 inversion process in general is extremely sensitive towards inner-sphere stabilization. Acta Chemica Scandinavica 1998.
- Lund, Torben,Jacobsen, Karin Bay
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p. 778 - 783
(2007/10/03)
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- Stereochemistries and mechanisms of reactions of electrophiles with organotin compounds
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The effect of solvent and electrophile on halodemetalation reactions of carbon-tin bonds has been investigated. Both stereochemical results and 119Sn NMR have been used as mechanistic probes. The effect of solvent is extreme; reactions performed in polar solvents such as acetonitrile and dimethylformamide yield cleavage products with predominantly inversion of configuration, whereas nonpolar solvents yield products with predominantly retention. Polar-aprotic solvents appear to be highly efficient in promoting inversion stereochemistry. Polar-protic solvents are not as efficient. This is explained in terms of some very specific solvation phenomena. Also, 119Sn NMR studies of several trialkyltin halides in various solvents show that these specific solvation phenomena can be qualitatively assessed. The nature of the electrophile also plays an important role in eventual stereochemistry; Br2, I2, ICl, and IBr are compared and discussed.
- Fukuto, Jon M.,Newman, David A.,Jensen, Frederick R.
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p. 415 - 420
(2008/10/08)
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