The biogenesis of rifamycin S

Propionic acids labelled either with ¹⁴C in positions 1, 2, or 3, or with ¹⁴C in position 1 and ³H in position 3 have been used as precursors in biosynthesis of rifamycins by Streptomyces mediterranei. The resulting distribution of radioactivity in rifamycins S – as determined by systematic degradation – shows that 23 of the 37 carbon atoms in rifamycin S originate from propionic acid. This result and the distribution pattern of radioactivity are in agreement with those obtained recently by ¹³C-NMR. spectroscopy [7]. The S-methyl groups of methionin, labelled with ¹⁴C, are incorporated in rifamycins by Streptomyces mediterranei only in the methoxy group. The consequences of these findings for the biogenesis of other ansamycins, e.g. streptovaricins, are discussed. The similarities in the constitution and configuration of ansamycins and macrolides (cf. [9]) indicate that all these microbial metabolites are formed according to the same biogenetic pattern.     

13C-NMR. Analysis of Dihydrogranaticin Methyl Ester. A case of mixed biogenesis

The ¹³C-NMR. spectrum of dihydrogranaticin methyl ester has been completely analyzed. Feeding experiments of CH₃ ¹³COONa to a culture of Streptomyces olivaceus have shown that only a sixteen carbon moiety of the antibiotic granaticin is of polyketide origin, thus confirming the hypothesis of a mixed biogenesis for this natural substance.     

Proposed biogenesis of diterpenoid alkaloids

Literature information is generalized and an analysis is made of investigations relating to the biogenesis of diterpene alkaloids.Institute of the Chemistry of Plant Substances, Academy of Sciences of the Republic of Uzbekistan, Tashkent, fax (3712) 89 14 75. Translated from Khimiya Prirodnykh Soedinenii, No. 3, pp. 337–354, May–June, 1995. Original article submitted May 18, 1993.     

Identification of putative proteins involved in granule biogenesis of tick salivary glands.

Ticks secrete bioactive components during feeding that assist them in gaining a blood meal. Compounds secreted are stored in granules until a stimulus induces secretion during feeding. Biogenesis of tick secretory granules has not been investigated before. An adequate understanding of granule biogenesis could advance our understanding of tick salivary gland biology and could aid in the rational design of tick control methods. Putative tick salivary gland proteins 1-4 (TSGP1-4) involved in granule biogenesis were identified in this study based on their abundance in salivary gland extracts and granule preparations and their ability to aggregate under conditions of slight acidity and high calcium concentration. TSGP2 and TSGP3 have been identified as previously described toxic and nontoxic homologues, respectively, while toxicity was also associated with TSGP4.     

On the biogenesis of gliotoxin. Synthesis of 3-(β-aminoethyl)benzene oxide.

The synthesis of 3-(β-aminoethyl)benzene oxide ($\text{7}$ is described. The failure of $\text{7}$ to ring close ($\text{7}$→$\text{8}$) is attributed to the low “nucleophilic susceptibility” of the arene oxide.     

Diterpenoids of mixed biogenesis in phaeophyta biogenetic-type interconversions

In the course of research into marine natural products, the diterpenoids taondiol 10 and atomaric acid 15, were isolated from the brown seaweed Taonia atomaria. The similarities of these structures plus the fact that both compounds come from the same alga suggest that there may be a biogenetic relationship between the two. This speculated relationship is adumbrated in Scheme 1, where the cyclic and acyclic diterpenoids of mixed biogenesis isolated from Phaeophyta are interrelated. In the present work, the competitive cyclisation of the proposed olefinic intermediate 4 to the naturally occurring compounds taondiol 10, isotandiol 11, epitaondiol 12 and stypodiol 13, is reported. The stereoselective transformation of atomaric acid 15 into the compound 4 is also reported, which transformation occurs by intramolecular carbocylisation of the olefinic aldehyde 7 followed by backbone rearrangement to the olefin 4. This result prompted the proposal that atomaric acid 15 may arise in nature by means of a like rearrangement but operating in a reverse direction.     

Enantiomeric natural products: occurrence and biogenesis

In nature, chiral natural products are usually produced in optically pure form-however, occasionally both enantiomers are formed. These enantiomeric natural products can arise from a single species or from different genera and/or species. Extensive research has been carried out over the years in an attempt to understand the biogenesis of naturally occurring enantiomers; however, many fascinating puzzles and stereochemical anomalies still remain.     

Khyberine and the biogenesis of dimeric aporphine-benzylisqoquinoline alkaloids

The new aporphine-benzylisquinoline khyberine ($\text{4b}$) is present in $\text{Berberis}$$\text{calliobotrys}$ Aitch. ex Bienert in about one part per million. An effort is made to present a complete scheme for the biogenesis of aporphine-benylisoquinoline dimers which arise from the condensation of two coclaurine units.     

Synthetic UDP-furanoses as potent inhibitors of mycobacterial galactan biogenesis

UDP-galactofuranose (UDP-Galf) is a substrate for two types of enzymes, UDP-galactopyranose mutase and galactofuranosyltransferases, which are present in many pathogenic organisms but absent from mammals. In particular, these enzymes are involved in the biosynthesis of cell wall galactan, a polymer essential for the survival of the causative agent of tuberculosis, Mycobacterium tuberculosis. We describe here the synthesis of derivatives of UDP-Galf modified at C-5 and C-6 using a chemoenzymatic route. In cell-free assays, these compounds prevented the formation of mycobacterial galactan, via the production of short "dead-end" intermediates resulting from their incorporation into the growing oligosaccharide chain. Modified UDP-furanoses thus constitute novel probes for the study of the two classes of enzymes involved in mycobacterial galactan assembly, and studies with these compounds may ultimately facilitate the future development of new therapeutic agents against tuberculosis.     

Reaction progress of chromophore biogenesis in green fluorescent protein

The mature form of green fluorescent protein (GFP) is generated by a spontaneous self-modification process that is essentially irreversible. A key step in chromophore biosynthesis involves slow air oxidation of an intermediate species, in which the backbone atoms of residues 65-67 have condensed to form a five-membered heterocycle. We have investigated the kinetics of hydrogen peroxide evolution during in vitro GFP maturation and found that the H2O2 coproduct is generated prior to the acquisition of green fluorescence at a stoichiometry of 1:1 (peroxide/chromophore). The experimental progress curves were computer-fitted to a three-step mechanism, in which the first step proceeds with a time constant of 1.5 (+/-1.1) min and includes protein folding and peptide cyclization. Kinetic data obtained by HPLC analysis support a rapid cyclization reaction that can be reversed upon acid denaturation. The second step proceeds with a time constant of 34.0 (+/-1.5) min and entails rate-limiting protein oxidation, as supported by a mass loss of 2 Da observed for tryptic peptides derived from species that accumulate during the reaction. The final step in GFP maturation proceeds with a time constant of 10.6 (+/-1.2) min, suggesting that this step may contribute to overall rate retardation. We propose that under highly aerobic conditions, the dominant reaction path follows a cyclization-oxidation-dehydration mechanism, in which dehydration of the heterocycle is facilitated by slow proton abstraction from the Tyr66 beta-carbon. In combination, the results presented here suggest a role for molecular oxygen in trapping the cyclized form of GFP.     

Comparative metabolomics reveals biogenesis of ascarosides, a modular library of small-molecule signals in C. elegans

In the model organism Caenorhabditis elegans, a family of endogenous small molecules, the ascarosides function as key regulators of developmental timing and behavior that act upstream of conserved signaling pathways. The ascarosides are based on the dideoxysugar ascarylose, which is linked to fatty-acid-like side chains of varying lengths derived from peroxisomal β-oxidation. Despite the importance of ascarosides for many aspects of C. elegans biology, knowledge of their structures, biosynthesis, and homeostasis remains incomplete. We used an MS/MS-based screen to profile ascarosides in C. elegans wild-type and mutant metabolomes, which revealed a much greater structural diversity of ascaroside derivatives than previously reported. Comparison of the metabolomes from wild-type and a series of peroxisomal β-oxidation mutants showed that the enoyl CoA-hydratase MAOC-1 serves an important role in ascaroside biosynthesis and clarified the functions of two other enzymes, ACOX-1 and DHS-28. We show that, following peroxisomal β-oxidation, the ascarosides are selectively derivatized with moieties of varied biogenetic origin and that such modifications can dramatically affect biological activity, producing signaling molecules active at low femtomolar concentrations. Based on these results, the ascarosides appear as a modular library of small-molecule signals, integrating building blocks from three major metabolic pathways: carbohydrate metabolism, peroxisomal β-oxidation of fatty acids, and amino acid catabolism. Our screen further demonstrates that ascaroside biosynthesis is directly affected by nutritional status and that excretion of the final products is highly selective.