Enzymatic assistance

The conversion of IT2CO8 and HCOa to CO2 is a very important biochemical proces which is enzymatically assisted in the lungs. 

Domingues et al. (160), in their comprehensive review of enzymatic improvement of oil extraction, included discussion of various processes that also used hexane as a solvent. They reported aqueous enzyme processes that used hexane in a 1 2 hexane-water ratio. Additional hexane was added to the enzyme-treated and dried materials. Although enzymatic-assisted extraction is presently only economical in olive processing, because of the milder conditions used and, in most cases, higher quality oils obtained, it does have potential for future use. 

In the case of 177b, compound 178b is formed and was isolated from the urine as the corresponding condensation product 179. Unlike 175b, other hydroxylation products were not observed. The instability of the Si-H bond of 177b in vivo may be explained by simple chemical hydrolysis, which does not require any enzymatic assistance however, from the experimental data available biological processes cannot completely be excluded. 

All compounds exhibit optical activity attesting to their enzymatically assisted generation. 

The isolated TE domain from the tyrocidine (tyc) NRPS has recently been shown to catalyze the macrocyclization of unnatural substrates to generate a variety of cyclic peptides. In conjunction with standard solid-phase peptide synthesis, Walsh and coworkers demonstrated a broad substrate tolerance for peptidyl-N-acetylcysteamine thioesters by the tyrocidine TE [41,42], Cyclization of peptide analogs, where individual amino acids were replaced with ethylene glycol units, was observed with high efficiency. In addition, hydroxyacid starter units were readily cyclized by the isolated TE domain to form nonribosomal peptide-derived macrolactones. More recently, Walsh and coworkers have demonstrated effective cyclization of PEGA resin-bound peptide/polyketide hybrids by the tyrocidine TE domain [43], Utilization of a pantetheine mimic for covalent attachment of small molecules to the resin, serves as an appropriate recognition domain for the enzyme. As peptide macrocyclizations remain challenging in the absence of enzymatic assistance, this approach promises facile construction of previously unattainable structures. 

Spurvey, S.A., Senanayake, S.PJ.N., and Shahidi, F. (2001) Enzymatic-Assisted Acidolysis of Menhaden and Seal Blubber Oils with y-Linolenic Acid, /. Am. Oil Chem. Soc. 78, 1105 1112. 

Investigations into avoid this danger have taken place. Extended anionic surfactants have been employed to extract corn oil instead of hexane [17]. These extractions were shown to extract 83% of the oil available and also maintained the composition of the corn oil when compared to extractions carried out using hexane. A mixture of enzymes to extract oil from Irvingia gabonensis kernels was employed controlled, ordered addition of the enzymes optimized the extraction of the oil up to 90% efficiency [18]. Similar protocols were applied to the extraction of canola oil [19] and showed that the enzymatically assisted extractions were more efficient than by using water alone and produced better oil quality than both aqueous and solvent extractions. The efficiency of the process in this instance was significantly increased from those previously stated (circa 25%). 

Importantly, though. Nature does not have to rely on enzymatic assistance in order to utilize the full range of synthetic power afforded by the Diels—Alder reaction since she can also construct compounds whose unsaturated motifs are disposed to participate spontaneously in this pericyclic reaction on their own accord. For instance, in the previous chapter on longithorone A, we chronicled how a transannular Diels—Alder reaction was initiated under ambient conditions the instant that a quinone-based dienophile was unveiled in a macrocyclic ring bearing a neighboring diene system. Similarly, as described in Chapter 17 of Classics /, heating a small... 

The solvent extraction can be enhanced by utilizing carbohydrate-hydrolyzing enzymes, for instance pectinase, cellulase, hemicellulase, and many other enzymes, which can be used to disintegrate the plant cell-wall matrix leading to more efficient release of phenolic compounds [36]. Enzymatic-assisted extraction has been applied for superior extraction of pol3q)henolic compounds from different biomaterials, such as black currant juice press residues [37, 38], pigeon pea leaves [39], and grape pomace [40]. 

The enzymatic tools for functionalization of chitin/chitosan are selected on the basis of the chemical structure of these biopolymers (functional groups and targeted enzyme activities related) and include oxidases, e.g., tyrosinase, peroxidase, laccase and transferase (transglutaminase) types of enzymes. The same enzymatically assisted reactions could be further employed to crosslink the functionalized biomaterials in order to improve their exploitation characteristics, i.e., stability at use. 

The earliest example of a biomimetic electrocyclisation cascade sequence in natural product synthesis is in Nicolaou s syntheses of the endiandric acids, isolated by Black in the early 1980s [15]. To explain the racemic nature of these natural products, Black proposed that they are formed spontaneously from achiral polyene precursors through non-enzymatically assisted electrocyclisation and cycloaddition cascades. In 1982 Nicolaou reported the synthesis of the methyl esters of all endiandric acids A-G in a one-operation cascade approach from linear polyene precursors [16]. The synthesis of endiandric acids A, D and E methyl esters (32, 30 and 31 respectively) is outlined below (Scheme 1.5). 

Ireland and Scheuer s experiments demonstrated that the in vivo photochemical transformation of 9,10-deoxytiidachione (2) into photodeoxytridachione (3) was non-enzymatic [17], suggesting that the origin of chirality in sacoglossan natural products, derived from achiral polyene precursors, does not lie in enzymatic assistance. 

For a longer period, a lot of work has been done to develop simultaneously aqueous, aqueous alcoholic or enzymatic-assisted extraction of oil, and protein from specific... 

Cueto M, D Croz L, Mate JL, San-Martin A, Darias J. Ely-siapyrones from Elysia diomedea. Do such metabolites evidence an enzymatically assisted electrocyclization cascade for the biosynthesis of their bicyclo[4. 2. 0]octane core Org. Lett. 2005 7 415 18. 

The first P-chiral hydroxy phosphoryl compounds that were enzymatically resolved into enantiomers were o-hydroxyaryl phosphines and their oxides 75. The resolution was achieved via enzyme-assisted hydrolysis of their O-acetyl derivatives 74, the most effective enzymes being CE and Upase from C. rugosa (CRL) (Equation 35). The highest enanfioselectivity was observed in the case of naphthyl derivatives (Equation 36), having a P=0 moiety. ... 

In the experiment involving oxidative enzyme HRP (EC 1.11.1.7, RZ 1.9, 240 purpuro gallin (units/mg)) [89] for the enzymatic treatment and ultrasonic waves of 423 kHz and 5.5 W, the phenol degradation rate was found to increase. The ultrasound assisted biodegradation method has been found to be more efficient method than the sonolysis and enzyme treatment when operated individually. 

A possible mechanism for this transformation, similar to the proposed enzymatic cleavage of carotenoids (Fig. 3), involves 0 = Ru = 0 porphyrin 21 catalyzed epoxidation of 17 to 22, followed by nucleophilic attack of TBHP and ring opening with assistance of 23. Subsequent fragmentation yields the aldehydes (Fig. 8). 

In MET, a low-molecular-weight, redox-active species, referred to as a mediator, is introduced to shuttle electrons between the enzyme active site and the electrode.In this case, the enzyme catalyzes the oxidation or reduction of the redox mediator. The reverse transformation (regeneration) of the mediator occurs on the electrode surface. The major characteristics of mediator-assisted electron transfer are that (i) the mediator acts as a cosubstrate for the enzymatic reaction and (ii) the electrochemical transformation of the mediator on the electrode has to be reversible. In these systems, the catalytic process involves enzymatic transformations of both the first substrate (fuel or oxidant) and the second substrate (mediator). The mediator is regenerated at the electrode surface, preferably at low overvoltage. The enzymatic reaction and the electrode reaction can be considered as separate yet coupled. 

Waldmann et al. developed a second exo-linker following a new approach [43-44] which makes use of a safety-catch linker. It is based on the enzymatic cleavage of a functional group embodied in the linker. In this way an intermediate is generated, which subsequently cyclizes intramolecularly according to the principle of assisted removal [54—58] and thereby releases the desired target compounds (Scheme 10.11). 

The versatility of polymer-assisted enzymatic synthesis of non-natural and biologically significant glycolipid derivatives was also demonstrated by constructing pseudo-ganglioside GM3, see K. Yamada, S. Matsumoto, S-I. Nishimura, Chem. Commun. 1999, 507-508. 

Xu, S., Pan, C., Hu, L., Zhang, Y, Guo, Z., Li, X., Zou, H. Enzymatic reaction of the immobilized enzyme on porous silicon studied by matrix assisted laser desorption/ionizationtime of flight-mass spectrometry. Electrophoresis 2004, 25, 3669-3676. 

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