Rearrangement enzymatic

Pseudomonine (Fig. 27, 76) is produced by Pseudomonas fluorescens strains (7, 228) and by P. entomophila, where it can act as a secondary siderophore (209). The substituents on C-4 and C-5 of the isoxazolinone ring are in trans positions (333). The complex formation has not been studied. In vitro enzyme-catalyzed synthesis studies (333,388) showed that initially the intermediate pre-pseudomonine (Fig. 24, 79) is formed, which non-enzymatically rearranges to pseudomonine. 

Pseudouridine is formed by enzymatic rearrangement of uridine in the original transcript (Eq. 28-3). It can form a base pair with adenine in the same manner as does uracil. Pseudouridine is found not only in tRNA but also in several places in both large and small ribo-somal RNA subunits. For example, it is present at position 516 in the E. coli 16S RNA,364 at a specific position in the 23S RNA, and at many more locations in eukaryotic rRNA. 

HAGMANN, M.-L., GRISEBACH, H., Enzymatic rearrangement of flavanone to isoflavone. FEBS Lett., 1984,175,199-202. 

The nonenzymatic 1,2-migration of an amino group in Scheme 1 is an efficient way to transform 2-methyl-3-bromoalanine ethyl ester into 2-methyl- alanine ethyl ester. It is possible that this nonenzymatic counterpart to the enzymatic rearrangement may serve as the foundation for an efficient synthetic transformation of a-amino acid derivatives into P-amino acid derivatives, which may in turn be of some use in the drug industry. Under conditions of low concentrations of tributyltin hydride in the process of Scheme 1, the ratio of P-amino acid ester to a-amino acid ester is 13/1, presumably because the radical 5 is more stable than 4 owing to the delocalization of the unpaired electron into the adjoining carboethoxy group. 

The role of coenzyme B12 as cofactor of enzymatic rearrangement reactions requires the (reversible) formation of the 5 -adenosyl radical by homolysis of the organometal-lic bond of (3) (estimated bond-dissociation energy ca. 30kcalmol to be accelerated there by a factor of... 

Formation of the thiocyanate (94) is believed to be caused by enzymatic rearrangement (E) of the isothiocyanate (54) although direct formation from the glucosinolate has not been excluded (95). It occurs in homogenized Eruca sativa plants but not seed (95), and in Lepidium sativum seed powder but not T. majus (54, 96). The isothiocyanate is initially (10-15 sec) formed in substantial quantities but immediately decreases to a low level (97, 98). Addition of mustard myrosinase to heated Lepidium seed powder produces only isothiocyanate (56). 

Prodrug activation occurs enzymatically, non-enzymatically, or sequentially (enzymatic step followed by non-enzymatic rearrangement). As much as possible, it is desirable to reduce biological variability, hence, the particular interest currently received by non-enzymatic reactions of intramolecular cyclization-eliminationf ... 

Another sugar substitute is palatinitol. The preparation of palatinitol uses sucrose as the starting material. After enzymatic rearrangement into palatinose (isomaltulose) and hydration, palatinitol is formed representing an equimolar mixture of the isomers a-D-glucopyranosido-1,6-mannitol and a-D-glucopyranosido-1,6-sorbitol ... 

Focus is also put on the third pathway which includes reactions of sucrose which lead to carbohydrate structures different from the starting carbohydrate sucrose. This includes the inversion of sucrose to the monomers o-glucose and o-fmctose but also enzymatic rearrangements of the two sucrose building blocks to other carbohydrates, e.g., isomaltulose and trehalulose. 

Trehalulose could be obtained by the enzymatic rearrangement of sucrose by Pseudomonas mesocacidophila [125-127]. Most characteristics of trehalulose are similar compared to those of palatinose. One main difference is the higher solubility of trehalulose which offers better opportunities regarding beverage appUcatiOTis [87, 125]. 

The Claisen rearrangement, which displays a negative activation volume, is also accelerated in water. Thus, the non-enzymatic rearrangement of chorismate to pre-phenate occurs 100 times faster in water than in methanol [55]. The accelerating... 

Conversion of arachidonic acid to an eicosanoid y-ketoaldehyde can proceed by two separate pathways, one driven enzymatically by cyclooxygenases and the other driven non-enzymatically by free radicals. The two pathways differ only in the mechanism used to generate the key intermediate, a bicyclic endoperoxide with two aliphatic side chains, which can undergo non-enzymatic rearrangement to... 

Rearrangements Reactions maintaining carbohydrate structure Inversion of sucrose to D-glucose and D-fructose is the simplest example, others -more complicated ones are the enzymatic rearrangements of the sucrose building blocks (D-glucose and D-fructose) into more complex carbohydrates. 

The rearrangement steps of B -dependent enzymatic rearrangements are now assumed to be accomphshed by tightly protein-bound radicals that are controlled in their reaction space [178,184,199] but (practically) unassisted by the Co(II)-corrin fragment of the coenzyme (which has a spectator role) [184,199]. In the coenzyme B -dependent enzymes, the main role of the bound cofactor thus is only the production and controlled presentation of the 5 -deoxy-5 -adenosyl radical from homolysis of the Co - C bond of AdoCbl (2), with little structural reorganization occurring in the cobalt-corrin part. 

In accordance with this assumption, it was observed by Berchtold and coworkersthat the non-enzymatic rearrangement of epi-chorismic acid to epi-prephenic acid is substantially faster than that of chorismic acid to prephenic acid. 

Enzymatic rearrangement of sucrose with Protoaminobacter rubrum CBS 574.77 performed on an industrial scale, affords isomaltulose (also named palatinose ) widely applied as artificial sweetener. Interesting optically pure derivatives (e.g. spiro-system f or analogs of nojirimycin 4) were obtained by hydrolysis of the glycosidic bond in functionalized sucroses. Sucralose (l, 4,6 -trideo)gr-l, 4,6 -trichloro-gaZarto-sucrose), prepared by chlorination of 6-0-acetylsucrose with S02Cl2/pyridine, represents an example in which the disaccharide skeleton is only slightly modified. 

Penicillin sulfoxide (349) has been reported to undergo enzymatic rearrangement by either Bacillus megaterium or Streptomyces venezuelae to a product having postulated structure 372 (Thomas, 1979). 

The transformation of bios5mthetically labelled 6-methyl-salicylate (from 2-i4C-acetate) into patulin, in 25 % radiochemical 5deld, was found to occur by Bassett and Tanenbaum (1959). The pattern of isotope distribution in the antibiotic harmonized fully with the oxidative molecular rearrangement hypothesis (Fig. 4). It was independently noted by Bu LOCKandRYAN (1958) that enzymatic rearrangement of radioactive 6-methylsalicylate biosynthetically obtained from acetate-1- C, also gave rise to the expected radioactivity distribution pattern in patulin. 

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