Acyclic monoesters

Acyclic monoesters of Table 11.1-2, which can be obtained with other hydrolases as such or of opposite configuration, are contained in Tables 11.1-7 and 11.1-12. 

Cyclic diesters are often even better substrates forlipases and esterases than acyclic derivatives. Small-ring monoacetates (28, n — 1-3) are obtained in higher yield and ee than the larger derivatives (for 28, n = 4 is only 50%) (43). Hydrolysis of tetrahydrofuran diester results in monoester (29) of ee > 99% (44). 

This ortho ester does not form a monoester upon deprotection as do acyclic ortho esters, thus avoiding a hydrolysis step. ... 

In a similar way, carbocycles having a quaternary center could be obtained from acyclic unsaturated 1,3-dicarbonyl compounds [206]. Other combinations are the domino hydroformylation/Wittig olefmation/hydrogenation described by Breit and coworkers [207]. The same group also developed the useful domino hydroformyla-tion/Knoevenagel/hydrogenation/decarboxylation process (Scheme 6/2.14) [208] a typical example is the reaction of 6/2-66 in the presence of a monoester of malonic acid to give 6/2-67 in 41 % yield in a syn anti-ratio of 96 4. Compounds 6/2-68 and 6/2-69 can be assumed as intermediates. 

The kinetic stability of monoesters and diesters is due largely to their negative charge when ionized, which repels nucleophiles. Thus, it is not surprising that as neutral compounds, triesters are the most reactive of the three classes of phosphate esters. A significant portion of the mechanistic studies on triesters have been carried out using six-membered ring cyclic triesters (Fig. 12).46 Such esters react at comparable rates to their acyclic counterparts, in contrast to five-membered cyclic phosphate esters, which react at much faster rates. 

A limited number of acyclic and cyclic prochiral dicarboxylic acid diesters were found to be good substrates for hydrolysis catalyzed by lipases (Table 11.1-12). Notable examples which give a good illustration of the potential of hydrolases as well as of the trial and error approach one relies on to a certain extent are the dithio acetal derivative 9 and the fluoro alkyl malonates 1-8. The dithio monoester 9 is obtained with different lipases with high enantioselectivities and yields despite its remote chiral center. Candida cylindracea lipase is the enzyme of choice for the synthesis of fluoro alkyl malonates with small alkyl groups. An astonishing observation was... 

The PDEs catalyze the hydrolysis of the 3 -phosphate diester bond of the cyclic nucleotides to give the acyclic 5 -phosphate monoesters (Fig. 17.1). They can be distinguished according to their primary structure, tissue distribution, intracellular localization, regulation, and specificity Families 4, 7, and 8 hydrolyze cAMP families 5, 6, and 9 hydrolyze cGMP and families 1, 2, 3, 10, and 11 hydrolyze both cyclic nucleotides (Table 17.1). 

Acyclic acid anhydrides react with alcohols (phenols) to give esters and carboxylic acids acid esters (monoesters) are formed from cyclic anhydrides ... 

Fig. 2. Phosphorus-31 chemical shift of phosphate esters versus O—P—O bond angle. , Five-membered cyclic esters A, monoester dianions x, monoester monoanions O, acyclic diester monoanions , acyclic diester free adds , sn-membeied cyclic esters. From Goren-stein (1975). Copyright 1975 American Chemical Sodety.

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