Rearrangement in biosynthesis

Meerwein Rearrangement Cascades ( Tandem Wagner-Meerwein Rearrangements ) in Biosynthesis... 

Possible involvement of aza-Cope rearrangement in biosynthesis of albine-type alkaloids... 

Fig. 8. Adelberg s scheme for aldol condensation of two molecules of pyruvate and pinacol rearrangement in biosynthesis of valine [modified from 1B7). ...

The pathways for thiamine biosynthesis have been elucidated only partiy. Thiamine pyrophosphate is made universally from the precursors 4-amino-5-hydroxymethyl-2-methylpytimidinepyrophosphate [841-01-0] (47) and 4-methyl-5-(2-hydroxyethyl)thiazolephosphate [3269-79-2] (48), but there appear to be different pathways ia the eadier steps. In bacteria, the early steps of the pyrimidine biosynthesis are same as those of purine nucleotide biosynthesis, 5-Aminoimidazole ribotide [41535-66-4] (AIR) (49) appears to be the sole and last common iatermediate ultimately the elements are suppHed by glycine, formate, and ribose. AIR is rearranged in a complex manner to the pyrimidine by an as-yet undetermined mechanism. In yeasts, the pathway to the pyrimidine is less well understood and maybe different (74—83) (Fig. 9). 

Werschkun B, Thiem J (2001) Claisen Rearrangements in Carbohydrate Chemistry. 215 293-325 Wiesler U-M, Weil T, Mullen K (2001) Nanosized Polyphenylene Dendrimers. 212 1-40 Williams RM, Stocking EM, Sanz-Cervera JF (2000) Biosynthesis of Prenylated Alkaloids Derived from Tryptophan. 209 97-173 Wirth T (2000) Introduction and General Aspects. 208 1-5 Wirth T (2003) Introduction and General Aspects. 224 1-4 Wirth T (2003) Oxidations and Rearrangements. 224 185-208 Wong MW, see Steudel R (2003) 230 117-134... 

Reaction type 6C (Table 10-1) occurs during the biosynthesis of leucine and valine (Fig. 24-17). The rearrangement is often compared with the nonenzy-matic acid-catalyzed pinacol-pinacolone rearrangement in which a similar shift of an alkyl group takes place (Eq. 13-57). The enzyme-catalyzed rearrangement... 

Hakamatsuka, T., Hashim, M.E., Ebizuka, Y. and Sankawa, U. (1991) P450-dependent oxidative rearrangement in isoflavone biosynthesis reconstitution of P450 and NADPH P450 reductase. Tetrahedron, 47, 5969-78. 

Terpenoids are widespread natural products that are formed from C5 isoprene units leading to their characteristic branched chain structure. Terpenoids are divided into families on the basis of the number of isoprene units from which they are formed. Thus there are monoterpenoids (Cio), sesquiterpenoids (C15) diterpenoids (C20), sesterterpenoids (C25), triterpenoids (C30) and carotenoids (C40). The isoprene units are normally linked together in a head-to-tail manner. However, the C30 triterpenoids and C40 carotenoids are formed by the dimerization of two Ci5 and C20 units, respectively. Hence, in these cases the central isoprene units are linked in a head-to-head manner. The presence of tertiary centres in the isoprenoid backbone of the terpenoids facilitates skeletal rearrangements in the biosynthesis of these natural products. As a consequence, on first inspection some structures appear not to obey the isoprene rule. 

Fission-rearrangement of epoxides. Following his suggestion that epoxy-acids may be important intermediates in biosynthesis,19 Gunstone with Conacher 20 found that when the unsaturated epoxy ester methyl vemolate (1) is treated with boron trifluoride etherate in cold benzene solution it is converted into a number of products, two of which cannot be separated from each other but, together, account for a yield of 34%. On the basis of chemical properties, infrared, NMR, and mass spectra they are believed to be the cis and trans forms of the ketocyclopropane ester (2). 

Terpenoids do not necessarily contain exact multiples of five carbons and allowance has to be made for the loss or addition of one or more fragments and possible molecular rearrangements during biosynthesis. In reality the terpenoids are biosynthesized from acetate units derived from the primary metabolism of fatty acids, carbohydrates and some amino acids (see Fig. 2.10). Acetate has been shown to be the sole primary precursor of the terpenoid cholesterol. The major route for terpenoid biosynthesis, the mevalonate pathway, is summarized in Fig. 2.16. Acetyl-CoA is involved in the generation of the C6 mevalonate unit, a process that involves reduction by NADPH. Subsequent decarboxylation during phosphorylation (i.e. addition of phosphate) in the presence of ATP yields the fundamental isoprenoid unit, isopentenyl pyrophosphate (IPP), from which the terpenoids are synthesized by enzymatic condensation reactions. Recently, an alternative pathway has been discovered for the formation of IPP in various eubacteria and plants, which involves the condensation of glyceraldehyde 3-phosphate and pyruvate to form the intermediate 1-deoxy-D-xylulose 5-phosphate (Fig. 2.16 e.g. Eisenreich et al. 1998). We consider some of the more common examples of the main classes of terpenoids below. 

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