Current Organic Chemistry - Volume 11, Issue 8, 2007

This latest issue of Current Organic Chemistry focusing on Bioorganic Chemistry is divided into six chapters written by experts in the fields of biotechnology and the bioorganic functions of fungi and their use in biotransformation and bio-catalytic processes. The first review by S.F. Arantes and J.R. Hanson presents an illustrative and authoritative account of the microbiological hydroxylation of some bridged polycyclic sesquiterpenoids by Mucor plumbeus in the context of defining the three dimensional topology of microbial hydroxylase. A three-dimensional model was constructed to rationalize the results and its use in a predictive sense is discussed. In the second review C. Hunter describes the current chemical utility of fungi in novel side chain formation, modification and degradation. This review focuses on three aspects of the application of marine and terrestrial filamentous fungi to sidechain chemistry from 2000 to early 2006: Generation of novel biologically active side-chains containing metabolites, the use of these fungi, both whole cell and lipases of fungal origin, in the chemical modification of side-chains and the degradation of side-chains by fungi. A. Garcia-Granados et al., provide a comprehensive and up-to-date review on the biotransformation studies of natural manoyl oxides and hemi-synthetic enantio-derivatives, carried out by means of biomimetic cyclization of ent-8-hydroxylabda- 13(16),14-dienes, with filamentous fungi. Along the same lines, Aleu et al. in the fourth contribution describe the use of isolated enzymes and microorganisms, especially fungi, as catalysts for the preparation of pheromones and their precursors. The role of endophytic fungi in plant-pathogen and plant-insect interactions is receiving increasing attention because of their potential use in pest control, however little is known about their physiology and the regulation processes of the plantendophyte interaction. An interesting perspective on endophytic fungi and their role in plant protection is reviewed by A. Gonzalez-Coloma et al. in the fifth chapter. In the sixth contribution, Barrero et al., provide a comprehensive review of the chemical structures of the secondary metabolites identified in Gibberella fujikuroi, with special attention to terpenoids, and particularly to gibberellins, and summarizes what is known about the biosynthesis of gibberellins, their regulation, and their relation to those of other metabolites. I am very pleased to have been involved as a Guest editor with this bioorganic issue of Current organic Chemistry and I would like to thank all of the authors who have contributed to this issue for their valuable and interesting contributions.

The regiospecificity of the microbiological hydroxylation of sesquiterpenoids by the fungus, Mucor plumbeus is reviewed. It is shown to fit a pattern which can be rationalized in terms of a model.

This review focuses on three aspects of the application of marine and terrestrial filamentous fungi to side-chain chemistry from 2000 to early 2006. The first section covers the generation of novel biologically active side-chain containing metabolites. This includes a range of antibiotic, cytotoxic and novel bioactive compounds. The second section discusses the use of these fungi both whole cell and lipases of fungal origin in the chemical modification of side-chains. Examples include reductive desymmetrization of pro-chiral ketones, dynamic kinetic resolution and unique reactions. The final section details the degradation of side-chains by fungi and includes lignin and steroid transformations for determination metabolism and the generation of new skeletal structure.

Microbial transformations of manoyl oxides by filamentous fungi have been used to introduce hydroxyl groups, regio- and stereoselectively, into substrates at positions difficult to achieve by chemical means. The principal objective of most papers published in this field has been to produce new, highly oxygenated, bioactive manoyl-oxide compounds that present a large diversity of biological properties. The manoyl oxides most frequently studied at present are forskolin and its derivatives, the pharmacological activity of which is related to their ability to activate AC (adenylate cyclase), thus generating an increase in intracellular cAMP (cyclic adenosine monophosphate). The microbial hydroxylation of forskolin and 1,9-dideoxyforskolin has been extensively studied, using the fungi Scopuloriopsis sp., Syncephalastrum sp., Neurospora crassa, Mortierella isabellina and several Aspergillus sp.. Other biotransformation studies of natural manoyl oxides and hemi-synthetic enantio derivatives, carried out via the biomimetic cyclization of ent-8α-hydroxylabda-13(16),14- dienes, have used filamentous fungi Curvularia lunata, Cunninghamella elegans, Fusarium moniliforme, Gibberella fujikuroi, Gliocladium roseum, Mucor plumbeus, Rhizopus nigricans and Neurospora crassa. In some cases, the new hydroxylations were introduced at the same positions as in natural forskolin, yielding some noteworthy products that show biological activities.

The application of biologically derived catalysts to the synthesis of agrochemicals has become increasingly popular in recent years. In most cases, the aim of using a biotransformation is either to introduce chirality into the molecule, to achieve a regioselective functionalization, or to selectively convert a functional group among other groups with similar reactivity. Pheromones, which have recently been commercialized as agrochemicals, are generally used in enantiopure forms with their intentional mixtures. Since they are usually highly effective, only very small quantities are needed to achieve the desired activity. This review, with approximately 200 references covering the period previous to December 2004, describes various efficient means of preparing optically pure pheromones and their precursors with the aid of isolated enzymes and microorganisms serving as catalysts.

Endophytes (fungal and bacterial organisms) have attracted great interest over the past few years because their presence benefits the host plant (development and defence) and they are a source of secondary metabolites of potential interest and thus play an important role in the regulation of plant communities and their herbivores. There are an increasing number of reports on their identification and on the production of secondary metabolites. Their role in plant-pathogen and plant-insect interactions is receiving increasing attention because of their potential use in pest control, however, little is known about their physiology and the regulation processes of the plant-endophyte interaction.

The rich metabolism of the fungal strains, now classified as Fusarium fujikuroi and related species covers the production of many secondary products, including different terpenoids and polyketides. Research has concentrated on the gibberellins, growth-promoting plant hormones with multiple applications in agriculture and brewing. The long list of secondary metabolites includes pigments such as carotenoids and bikaverins, mycotoxins such as fusarins and fumonisins and a diversity of other compounds, many of them still being unidentified. This review describes the chemical structures of the secondary metabolites identified in these fungi, with special attention to the terpenoids and particularly to the gibberellins, and summarizes knowledge on the biosynthesis of gibberellins, its regulation and its relation to those of other metabolites.