Enzymatic O-methylation

Catechol-O-Methyltransferase. Figure. 1 The basic function of COMT. Enzymatic O-methylation of the catechol substrate to 3-methoxy (major route) or 4-methoxy (minor route) products in the presence of Mg2+ and S-adenosyl-methionine (AdoMet). 

Enzymatic O-methylation of flavonoids, which is catalyzed by O-methyltransferases (E.C. 2.1.1.6-) involves the transfer of the methyl group of an activated methyl donor, S -adenosyl-L-methionine, to the hydroxyl group of a flavonoid acceptor with the formation of the corresponding methylether and S -adenosyl-L-homocysteine. The latter product is, in... 

Axelrod, Julius, and Robert Tomchick. 1958. "Enzymatic O-Methylation of Epinephrine and Other Catechols." Journal of Biological Chemistry 233 702-5. 

Axelrod, J. and Tomchick, R., Enzymatic O-methylation of epinephrine and other catechols, J. Biol. Chem. 233, 702 (1958). 

As described above, the enzymatic polymerization of phenols was often carried out in a mixture of a water-miscible organic solvent and a buffer. By adding 2,6-di-0-methyl-(3-cyclodextrin (DM-(3-CD), the enzymatic polymerization of water-insoluble m-substituted phenols proceeded in buffer. The water-soluble complex of the monomer and DM-(3-CD was formed and was polymerized by HRP to give a soluble polymer. In the case of phenol, the polymerization took place in the presence of 2,6-di-O-methyl-a-cyclodextrin (DM-a-CD) in a buffer. Only a catalytic amount of DM-a-CD was necessary to induce the polymerization efficiently. Coniferyl alcohol was oxidatively polymerized in the presence of a-CD in an aqueous solution. ... 

A series of subsequent reactions after PAL first introduces a hydroxyl at the 4-position of the ring of cinnamic acid to form p- or 4-coumaric acid (i.e., 4-hydroxycinnamic acid). Addition of a second hydroxyl at the 3-position yields caffeic acid, whereas O-methylation of this hydroxyl group produces ferulic acid (see Fig. 3.3). Two additional enzymatic reactions are necessary to produce sinapic acid. These hy-drocinnamic acids are not found in significant amounts in plant tissue because they are rapidly converted to coenzyme A esters, or glucose esters. These activated intermediates form an important branch point because they can participate in a wide range of subsequent reactions. 

Figure 1. Postulated pathway for the enzymatic synthesis of polymethylated flavonol glucosides in Chrysosplenium americanum GT, O-glucosyl-transferase OH, hydroxylase OMT, O-methyl transferase.

Galbis et al. described a variety of carbohydrate-based linear polyesters 61 of the poly(alkylene dicarboxylate) type that were obtained by polycondensation reactions of the alditols 2,3,4-tri-(9-methyl-L-arabinitol (9) and 2,3,4-tri-O-methyl-xylitol (10), and the aldaric acids 2,3,4-tri-(9-methyl-L-arabinaric acid (26) and 2,3,4-tri-(9-methyl-xylaric acid (27), butanediol, and adipic acid were also used as comonomers [28]. Copolyesters of the poly(aIkylene-c )-arylene dicarboxylate) type were obtained using bisphenols as comonomers (Scheme 1). Chemical polycondensation reactions were conducted in bulk or in solution. Enzymatic polycondensation reactions of adipic acid with the above-mentioned alditols were carried out successfully using Lipozyme and Novozyme 435. The hydrolytic degradations of some of these polyesters were also described. 

Figure 25. Trace enantiomer analysis of L-aspartic acid (obtained by enzymatic amination of fumarate with L-aspartase and determined as the A -trifluoroacetyl-O-methyl ester) on i.-Chirasil-Val31 [20 mx0.25 mm (i.d.) glass capillary column, 90 CC, 0.4 bar hydrogen] with detection by GLC MS selected ion monitoring (mj 198.1) and multiscanning chromatography (MSC, 8 scans)186.

Recently, Senoh, Tokuyama, and Witkop (37) have studied a metal-activated enzymatic reaction in the presence and the absence of enzyme, and have discovered that the order of effectiveness of the metals is exactly the reverse in the enzymatic and nonenzymatic processes. The reaction was O-methylation of 3,4-dihydroxybenzaldehyde. In the absence of divalent metal ions, the nonenzymatic reaction yields very predominantly the paramethylated product in neutral solution, since the p-hydroxyl group is the more electronegative. Metal complex formation... 

The structure of alpha-0 is designed to overcome these two restrictions. A methyl group on the oxygen (the O-methyl) removes the polarity restriction. A methyl group next to the amine function (the alpha-methyl) protects the molecule from enzymatic attack. With the two obstacles removed, this compound apparently has easy access directly to the brain. Hence, alpha,O-dimethylserotonin (a,0-DMS) goes directly into the central nervous system and has proved to be one of the most potent tryptamines yet described. And it is active following oral administration, where it is exposed to all of the body s protective machinery. 

R. L. Halcomb, W. Fitz, and C.-H. Wong, Enzymatic synthesis of 7-deoxy-A/-acetylneuraminic acid and 7-O-methyl-N-acetylneuraminic acid, Tetrahedron Asymm. 5 2437 (1994). 

VX appears to follow a similar pathway, the major metabolite being ethyl MPA (EMPA). An additional metabolite, derived from the diisopropy-laminoethyl substituent, was identified in human plasma following an assassination with VX (45). The sulfide (17), derived from enzymatic S-methylation of the hydrolysis product HSCH2CH2N(i-Pr)2, was identified in human serum by GC/MS after simple extraction. Experiments in rats confirmed the rapid metabolic formation of (17) from HSCH2CH2N(i-Pr)2 (46). Identification of this metabolite distinguishes VX from the O-ethyl analogue of sarin. 

KAMMERER, L., DE-EKNAMKUL, W ZENK, M.H., Enzymatic 12-hydroxylation and 12-O-methylation of dihydrochelirubine in dihydromacarpine formation by Thalictrum bulgaricum. Phytochemistry, 1994,36, 1409-1416. 

With the assumption that reticulines are also precursors in mammalian synthesis of morphine, it was challenging to investigate whether they could be produced by enzymatic reactions similar to those utilized in benzylisoquinoline-producing plants (274). This plan focused attention on reactions controlled by the enzyme catechol 0-methyltransferase (COMT), using 5-adenosyl-L-methionine (SAM) for the methylation reaction. Mammalian COMT is present in mammalian tissues, particularly the liver, and an enzyme preparation from rat liver was used for the experiments. It was found that (S)-norcoclaurine, which is the first isoquinoline produced in benzylisoquinoline-producing plants, was similarly O-methylated in vitro by SAM in the presence of COMT, and a reverse proportion of methylated products was obtained with the (/ )-enantiomer (277). Similar 0-methylation of (5)-4 -demethylreticuline (3 -hydroxy-N-methylcoclaurine), prepared by total synthesis (162), however, afforded almost exclusively (5)-orientaline, with a methoxy group at C-3 and not at C-4 as in (5)-reticuline (Fig. 37) (762). 

Incorporated as a dienophile. These results strongly indicate that dehydrogenation at the isoprenyl portion of (48) followed by a [4 2]cycloaddition reaction with the a, p-double bond of another molecule of isoprenylchalcone leads to the formation of the Diels-Alder type metabolites. Furthermore, the Diels-Alder type metabolites from the precursory chalcones (47), (48), and (53) are all optically active, having the same stereochemistries as those of )cuwanon J (11) and chalcomoracin (21). This fact revealed the [4 + 2]cycloaddition step to be enzymatic. Administration of O-methylated precursory chalcone to the M. alba cell cultures has thus demonstrated that optically active mulberry Diels-Alder type adducts such as 11 and 21 are biosynthesized through an enzymatic intermolecular [4 + 2Jcycloaddition reaction. 

Discovery. The majority of both old and new antidepressants act by virtue of their ability to inhibit monoamine transporter mechanisms in the brain. The concept that neurotransmitters are inactivated by uptake of the released chemical into the nerve terminal from which it had been released or into adjacent cells is less than 40 years old. Before this it was generally assumed that the inactivation of norepinephrine and the other monoamine neurotransmitters after their release from nerves was likely to involve rapid enzymatic breakdown, akin to that seen with acetylcholinesterase. The degradation of monoamines by the enzyme monoamine oxidase vas known early on, and in the 1950s a second enzyme catechol-O-methyl transferase (COMT) vas discovered and was thought to play a key role in inactivating norepinephrine and other catecholamines. 

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