Enzymatic cleavage amines

The fhioethyl group present in the anchor group of (40) was activated by treatment with N-iodosuccinimide (NIS) followed by displacement with a variety of alcohols (44-46). To prove the possible application of this linker in solid phase carbohydrate synthesis, protected glycosides (47) and (48) were coupled to linker (40) and released enzymatically. Flitsch et al. also described the immobilization and enzymatic cleavage on a variety of amines [41]. Nevertheless, the application of this enzyme-labile hnker group in multi-step syntheses on the solid phase and subsequent enzyme-initiated release from the polymeric support has not been described yet. 

Grether and Waldmann [15] developed an enzyme-labile safety catch linker 1 tested in intermolecular Mizoroki-Heck reactions (Scheme 14.1). This linker releases alcohols and amines through enzymatic cleavage of the benzylamide moiety followed by snbsequent lactam formation. After a Mizoroki-Heck reaction performed on an immobilized iodoarene... 

Phenylacetic acid offers interesting prospects for the production of pure stereo-isomeric amine compounds. This involves splitting the mixed amines in the form of DL-amides of phenylacetic acid with enzymes, when only the L-form is affected by the enzymatic cleavage, so that the stereoisomeric amines can be separated. 

Another interesting target for this type of inhibitors is the dipeptidyl peptidase IV (DPP IV). This exodipeptidase, which can cleave peptides behind a proline residue is important in type 2 diabetes as it truncates the glucagon-like peptide 1. Taking into account the P2-Pi( Pro)-P,1 cleavage and the requirement for a free terminal amine, the synthesis of a suicide inhibitor was planned. It looked as if the the e-amino group of a P2 lysine residue could be cyclized because of the relative little importance of the nature of the P2 residue on the rate of enzymatic hydrolysis of known synthetic substrates. Therefore, anew series of cyclopeptides 11 was synthesized (Fig. 11.8). 

The yeast-mediated enzymatic biodegradation of azo dyes can be accomplished either by reductive reactions or by oxidative reactions. In general, reductive reactions led to cleavage of azo dyes into aromatic amines, which are further mineralized by yeasts. Enzymes putatively involved in this process are NADH-dependent reductases [24] and an azoreductase [16], which is dependent on the extracellular activity of a component of the plasma membrane redox system, identified as a ferric reductase [19]. Recently, significant increase in the activities of NADH-dependent reductase and azoreductase was observed in the cells of Trichosporon beigelii obtained at the end of the decolorization process [25]. 

AT-[(Acyloxy)methyl] derivatives of active amines and amides have the general formula RK N-CHR O-COR " where R" = H or Me (or an even larger substituent) and COR" is the acyl group. Activation of these derivatives occurs in two steps as depicted in Fig. 8.20, by analogy with the biotransformation of 0-[(acyloxy)methyl] derivatives of phenols (Sect. 8.5.6) [62], The first step is enzymatic or nonenzymatic cleavage of the ester bridge (Fig. 8.20,a), followed by chemical breakdown of the A-(hydroxymethyl) intermediate (see also Chapt. 5 in [81]). Here, again, liberation of toxic formaldehyde, i. e., where R" = H, should be avoided whenever possible by substitution of, e.g., Me at R"... 

Fig. 8.20. Two-step activation ofN-[(acyloxy)methyl] prodrugs, a) Cleavage of the ester bond, which may be enzymatic and/or nonenzymatic, is followed by decomposition of the N-(hy-droxymethyl) intermediate, b) For (V-(hydroxymethyl) derivatives of amides and imides, the decomposition is base-catalyzed, c) For N-(hydroxymethyl) derivatives of amines, the decomposition can be uncatalyzed or undergo acid or base catalysis (modified from [214]).

Vanillylamine [(4-hydroxy-3-methoxy-phenyl)methylamine] is the substrate of choice for the formation of vanillin with the help of amine oxidase. It can be obtained by cleavage of capsaicin (N-[(4-hydroxy-3-methoxy-phenyl)methyl]-8-methyl-6-nonenamide) isolated from pepper and capsicum [83]. As natural vanillin extracted from beans of Vanilla planifolia is rare and extremely expensive, this pathway for the production of natural vanillin is regarded to have a great potential. The vanillin obtained by the process can be labelled as natural if the cleavage of capsaicin is performed enzymatically. 

Table 3.26 lists illustrative examples of cleavage reactions of support-bound N-aryl-carbamates, anilides, and /V-arylsulfonamidcs. /V-Arylcarbamatcs are more susceptible to attack by nucleophiles than /V-alkylcarbamates, and, if strong bases or nucleophiles are to be used in a reaction sequence, it might be a better choice to link the aniline to the support as an /V-bcnzyl derivative. Entry 7 (Table 3.26) is an example of a safety-catch linker for anilines, in which activation is achieved by enzymatic hydrolysis of a phenylacetamide to liberate a primary amine, which then cleaves the anilide. 

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