Micro-organisms have been isolated that can utilize o-coumaric acid as a sole carbon source with the subsequent production of 4-hydroxycoumarin and dicoumarol. One of these organisms, Penicillium jenseni, has been used to examine the biosynthesis of dicoumarol. Certain thermophilic fungi have also been found that can convert o-coumaric acid into dicoumarol.
A series of mono-and di-ortho-substituted benzoylcholine compounds has been prepared and the rates of hydroxide ion and cholinesterase catalysed hydrolysis has been determined for each compound. The anti-acetylcholinesterase activities of the compounds have also been determined. It has been found that some of the compounds are stable to esterase catalysed hydrolysis and that the groups which confer stability do not prevent the formation of enzyme substrate complexes. The most suitable groups for ester stabilisation, when used as ortho substituents, are alkyl and iodo as mono substituents and most groups, except hydroxy, as di-ortho substituents.THE in vivo hydrolysis of benzoyl ester groups is a limiting factor in the use of some drugs and consequently it would be of value to stabilise such esters. The hydrolysis of benzoylcholine is catalysed both by hydroxide ions and by serum cholinesterase and therefore this molecule is suitable to examine the influence of ortho substitution on esterase catalysed hydrolysis of benzoyl esters. Ormerod (1953) prepared several meta and para substituted benzoylcholine compounds and determined their rates of cholinesterase catalysed hydrolysis. The small differences observed between experimental results and results calculated using the Hammett substituent constant were attributed to "differences in the enzyme substrate complex".Ortho substituents in benzoate esters have been shown (Evans, Gordon and Watson, 1937;Ingold, 1953a) to accelerate less or retard more the rate of ester hydrolysis than the same substituents in the meta and para positions. Consequently, ortho substitution of benzoylcholine may produce large changes in the rates of cholinesterase catalysed hydrolysis.The interactions between an ester group and an ortho substituent may be direct or transmitted or a combination of both these effects. The direct effect is exerted by way of electrostatic forces, van der Waal's forces and short range repulsive forces. The effects of the latter forces have been termed the primary steric effect (Ingold, 1953b). Transmitted interactions are due to induction and mesomerism. Where steric repulsion alters the geometry of a molecule, thereby modifying the transmitted interactions, the effect has been termed the secondary steric effect (Ingold, 1953~).Bender (1951) demonstrated the presence of a tetrahedral intermediate of the type I in the acid and alkali catalysed hydrolysis of esters.
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