Biosynthetic studies

Strategy Problem 6 A labelled compound for biosynthetic studies. Mevaloitic acid (TM 418) is an intermediate in the biosynthesis of terpenes and steroids (Tedder, volume 4, p.217 ff). To study exactly what happens to each carbon atom during its transformation into, say, hmonene (418A), we need separate samples of mevalonic acid labelled with in each carbon atom in the molecule. This turns our normal strategy on its head since we must now look for one carbon discoimections. You can use reagents like Na CN, and... 

Biosynthetic studies using acetate (Ac), propionate (Pr), and butyrate (Bu) revealed the polyketide nature of aurodox which has the composition Pr(Ac)g for the goldinamine skeleton C-7 to C-25 and the composition Bu(Ac) for the C-27 to C-39 carbon chain of goldinonic acid. In contrast to the methyl branch at C-8, those at C-19 and C-21 are methionine-derived as are all remaining methyl groups (52,53). The biogenetic origin of the pyridone moiety is not clear. 

Most of the naturally-occurring pyrazine hydroxamic acids appear to be derived from valine, leucine and isoleucine, and biosynthetic studies by MacDonald and coworkers (61JBC(236)512, 62JBC(237)1977, 65JBC(240)1692) indicate that these amino acids are incorporated. However, it would seem that the logical intermediates, viz. the 2,5-dioxopiperazines such as (111) and (112), are not always incorporated. This does not rule out their intermediacy, as there may be problems such as low solubility or membrane permeability which prevent their efficient incorporation. An exception to these results was reported for pulcherrimic acid (113) (65BJ(96)533), which has been shown to be derived from cyclo-L-leu-L-leu which serves as an efficient precursor. 

L-jS-Pyrazolylalanine (755) and y-L-glutamyl-/8-pyrazol-L-alanine are found in the seeds of many speeies of Cucurbitaceae (65P933). It was subsequently demonstrated that free pyrazole oeeurs in watermelon seeds in eoneentrations of 280 to 410 jLg g depending on the variety (75P2512). Biosynthetic studies implieate 1,3-diaminopropane as a precursor of the pyrazole moiety of (755) (82P863). 

S,3S)-Dicarboxyaziridine (112) was isolated from a Streptomyces strain in 1975 and found to have moderate antibacterial activity against Aeromonas salmonecida [176]. Subsequent studies showed that 112 acts as a competitive inhibitor of fumar-ase, through mimicry of a carbanionic transition state [177]. No biosynthetic studies have been reported for 112, but it is conceivable that it may arise from cydiza-tion of (3R)-hydroxyaspartic acid (Figure 11.18). 

Epoxyfarnesol was first prepared by van Tamelen, Stomi, Hessler, and Schwartz 4 using essentially this procedure. It is based on the findings of van Tamelen and Curphey5 that N-bromosuccinimide in a polar solvent was a considerably more selective oxidant than others they tried. This method has been applied to produce terminally epoxidized mono-, sesqui-, di-, and triterpene systems for biosynthetic studies and bioorganic synthesis.6 It has also been applied successfully in a simple synthesis of tritium-labeled squalene [2,6,10,14,18,22-Tetracosahexaene, 2,6,10,15,19,23-hexamethyl-, (all-E)-] and squalene-2,3-oxide [Oxirane, 2,2-dimethyl-3-(3,7,12,16,20-pentamethyl-3,7,ll,-15,19-heneicosapentaenyl)-, (all-E)-],7 and in the synthesis of Cecropia juvenile hormone.8... 

Finally, the necessity arose for the synthesis of pentulose 21, labeled with, 3C on the central carbons, C-2 and C-3, for an independent biosynthetic study, which is reported in Section III.5.27 The doubly labeled ester 34 (Scheme 14) is readily available by a Wittig- Homer condensation of benzyloxyacetaldehyde with commercially available triethylphosphono-(l,2-l3C2)acetate. Chirality was introduced by the reduction of ester 34 to the allylic alcohol, which produced the chiral epoxide 35 by the Sharpless epoxidation procedure. This was converted into the tetrose 36, and thence, into the protected pentulose 37 by the usual sequence of Grignard reaction and oxidation. 

Glycoproteins occur in most organisms, from bacteria to humans. Many vimses also contain glycoproteins, some of which have been much investigated, in part because they are very suitable for biosynthetic studies. Numerous proteins with diverse functions are glycoproteins (Table 47-1) their carbohydrate content ranges from 1% to over 85% by weight. 

Staunton J, AC Sutkowski (1991) NMR in biosynthetic studies aspyrone, asperolactone isoasperoloac-tone, metabolites of Aspergillus melleus. J Chem Soc Chem Commun 1106-1108. 

This recyclization reaction has been skillfully utilized for stereospecific labeling at C-13 of tetrahydroberberine with tritium or deuterium for biosynthetic studies of ophiocarpine (20). Base A- and B-type products have... 

Regioselective 9-O-demethylation of 15 was achieved by pyrolysis at 190°C to give berberrubine (71) (Scheme 17) (55), and 64 was similarly converted to palmatrubine (72), which was derivatized to [9-0-methyl-14C] palmatine for biosynthetic studies (59). 

Labeled muramine (395) was synthesized for biosynthetic studies from tetrahydropalmatine (27) in 35% overall yield via the von Braun reaction product 30c (Section II,A,2) and the alcohol 403 (Scheme 76) (42). Labeled 13-oxygenated muramines 405a and 405b were obtained by oxidation of dihydropalmatine metho salt (404) with osmium tetroxide (42). 

During the period 1976-1986, biosynthetic studies on hasubanan alkaloids were carried out by Battersby et al. (81-84) for hasubanonine (5) together with protostephanine (57). The two alkaloids, isolated from Stephania japonica, arise from the same precursor, and their unusual structures are of biosynthetic interest, namely, the vicinally trioxygenated ring C in 5 and the unique natural example of a dibenz d,f ] azonine skeleton in 57. 

Biosynthetic studies of A2E, a major fluorophore of RPE lipofuscin. J Biol Chem. 277, 7183-7190. Bhosale, P, Larson, A.J., Frederick, J.M., Southwick, K., Thulin, C.D., Bernstein, P.S., 2004. Identification and characterization of a Pi isoform of glutathioine S-transferase (GSTP1) as a zeaxanthin-binding protein in the macula of the human eye. J Biol Chem. 279, 49447 19454. 

The structure elucidation of the kinamycins was a formidable challenge, and the information presented below draws from the work of several research groups over a period of more than 20 years. As will be shown, the originally proposed structure of the kinamycins contained a cyanamide rather than a diazo function. Subsequent synthetic and biosynthetic studies led to replacement of the cyanamide with a diazo function. The structural elucidation was challenging, in part, because of the high degree of unsaturation of the kinamycins, which limits the utility of H and 2D NMR analysis. In addition, because these structures were unprecedented, there were no clear benchmarks for comparison at the time. The pathway from isolation to determination of the correct structure is described below. 

A comprehensive compilation of data derived from feeding and other biosynthetic studies performed by Kirby [21], Sammes [22], and Taylor [23], genomic studies conducted by Howlett [lc, 24], as well as our own synthetic studies probing the innate reactivity of various intermediates (vide infra) culminated in our formulation of the biosynthetic hypothesis delineated below (Scheme 9.1). The biosynthesis features two distinct phases an oxidative dimerization phase and a thiolation phase in which diketopiperazine structures are elaborated to afford the defining epipolysulfide motifs (Scheme 9.1) [25, 26]. 

Use of encapsulated labeled precursors in lipid vesicles enabled the Hawaiian group to conduct the biosynthetic studies - with the exception of workup of the sponge - entirely in the field. Incorporation of doubly labeled [13C, 15N]cyanide into a Ciocalypta sp. and an Acanthella sp. produced labeled 9-isocyanoneopupukeanane (77) and kalihinol-F (112) respectively [71]. Detection of incorporation was followed by 13C NMR experiments. 

Throughout this chapter a major emphasis is given to recent work, since the biosynthesis of molluscan secondary metabolites has been partly covered in previous reviews [8, 9] devoted to the entire field of the biosynthetic studies on marine natural products. 

The problems associated with biosynthetic studies on marine organisms have been elaborated by Garson [9], They essentially derive from our still limited understanding of metabolic processes in the marine environment. 

Virtually all biosynthetic studies with molluscs have been conducted using precursors labelled with radioisotopes. In general, experiments are carried out... 

GERSHENZON, J., McCASKILL, D., RAJAONARIVONY, J.I.M., MIHALIAK, C., KARP, F., CROTEAU, R., Isolation of secretory cells from plant glandular trichomes and their use in biosynthetic studies of monoterpenes and other gland products, Anal. Biochem., 1992, 200, 130-138. 

Melikian, H. E., McDonald, J. K., Gu, H., Rudnick, G., Moore, K. R., and Blakely, R. D. (1994) Human norepinephrine transporter. Biosynthetic studies using a site-directed polyclonal antibody. J. Biol. Chem. 269,12290-12297. 

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