Enzymatic cleavage acetates

The Shen group has devised a domino process wherein after an enzymatic cleavage of a glycoside a rearrangement sequence takes place [18]. Subjecting multifloroside 8-38 to P-glucosidase in acetate buffer (Scheme 8.10) afforded jasmolac-tone analogues such as 8-39 in a rather low yield. 

In no instance did the synthetic retinoid possess as great an inhibitory capacity as do retinol or retinyl acetate. In addition, the provitamin g-carotene had no effect on mutagenicity of 2-fluorenamine in Salmonella regardless of the carcinogen activation system (Tables III and IV). Thus, 3-carotene would apparently require enzymatic cleavage to vitamin A in order to have an effect in this ijri vitro bioassay and exerts no role by itself in modulating the metabolism of chemical carcinogens in the model system. 

FIGURE 16.9 Anticancer drug paclitaxel 33. (A) Enzymatic cleavage of the C-13 side chain from taxanes. (B) Enzymatic cleavage of the C-10 acetate from taxanes. (C) Enzymatic cleavage of the C-7 xylosyl groups from taxanes. 

Imidazolone propionate hydrolase catalyzes the enzymatic cleavage of the imidazole ring to yield formi-minoglutamate. The rat liver enzyme has been partially purified. In addition to the enzymic conversion, two nonenzymic spontaneous reactions yield N-formyl-isoglutamine and 4-oxoglutamic acid. In addition to the oxidative pathways for histidine, there exist three other pathways for its use protein synthesis, decarboxylation to yield histamine (see Inflammation), and transaminase. The activity of histidine pyruvic transamination in rat liver is three times that of histidase. The product of the transaminase reaction is imidazole pyruvic acid, which in turn is converted to imidazole acetic acid. 

A similar semisynthetic method involves pronase E cleavage of leupeptin dibutyl acetal.157 Leupeptin dibutyl acetal has been prepared, cleaved by pronase E, and depro-tected as in the case of thermolysin, except pronase E cleaves the Leu-Arg bond instead of the Leu-Leu bond, thus affording H-Arg[CH(OBu)2]. This enzymatic technique was applied for the semisynthesis of Z-Val-Pro-Arg-Hj57 Again, the peptide dibutyl acetals can be treated with acid to afford the aldehydic leupeptin analogues with good yields and stereochemical conservation. 

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