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Issue 3, 2012
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peri-Dimethylamino substituent effects on proton transfer at carbon in α-naphthylacetateesters: a model for mandelate racemase

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Abstract

The rate constants for exchange of hydrogen for deuterium at the α-CH2 positions of 8-(N,N-dimethylaminonaphthalen-1-yl)acetic acid tert-butyl ester 1 and naphthalen-1-ylacetic acid tert-butyl ester 2 have been determined in potassium deuteroxide solutions in 1 : 1 D2O : CD3CN, in order to quantify the effect of the neighbouring peri-dimethylamino substituent on α-deprotonation. Intramolecular general base catalysis by the (weakly basic) neighbouring group was not detected. Second-order rate constants, kDO, for the deuterium exchange reactions of esters 1 and 2 have been determined as 1.35 × 10−4 M−1 s−1 and 3.95 × 10−3 M−1 s−1, respectively. The unexpected 29-fold decrease in the kDO value upon the introduction of a peri-dimethylamino group is attributed to an unfavourable steric and/or electronic substituent effect on intermolecular deprotonation by deuteroxide ion. From the experimental kDO values, carbon acid pKa values of 26.8 and 23.1 have been calculated for esters 1 and 2.

Graphical abstract: peri-Dimethylamino substituent effects on proton transfer at carbon in α-naphthylacetate esters: a model for mandelate racemase

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Article information


Submitted
05 Sep 2011
Accepted
11 Oct 2011
First published
11 Oct 2011

Org. Biomol. Chem., 2012,10, 590-596
Article type
Paper

peri-Dimethylamino substituent effects on proton transfer at carbon in α-naphthylacetate esters: a model for mandelate racemase

R. J. Delley, S. Bandyopadhyay, M. A. Fox, C. Schliehe, D. R. W. Hodgson, F. Hollfelder, A. J. Kirby and A. C. O'Donoghue, Org. Biomol. Chem., 2012, 10, 590
DOI: 10.1039/C1OB06525D

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