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peri-Dimethylamino Substituent Effects on Proton Transfer at Carbon in α-naphthylacetate Esters: A Model for Mandelate Racemase

peri-Dimethylamino Substituent Effects on Proton Transfer at Carbon in α-naphthylacetate Esters: A Model for Mandelate Racemase

Richard J Delley, Subhajit Bandyopadhyay, Mark A Fox, Constanze Schliehe, David R W Hodgson, Florian Hollfelder, Anthony J Kirby, AnnMarie C O'Donoghue

Org Biomol Chem. 2012 Jan 21;10(3):590-6.

PMID: 22108698

Abstract:

The rate constants for exchange of hydrogen for deuterium at the α-CH(2) 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 D(2)O : CD(3)CN, 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, k(DO), 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 k(DO) 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 k(DO) values, carbon acid pK(a) values of 26.8 and 23.1 have been calculated for esters 1 and 2.

Chemicals Related in the Paper:

Catalog Number	Product Name	Structure	CAS Number	Price
AP24572018	Potassium deuteroxide solution		24572-01-8	Price

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