Biosynthesis of Gabosines A, B, and C, Carba Sugars fromStreptomyces cellulosae

Biosynthesis and Biological Activity of Carbasugars

The first synthesis of carbasugars, compounds in which the ring oxygen of a monosaccharide had been replaced by a methylene moiety, was described in 1966 by Professor G. E. McCasland’s group. Seven years later, the first true natural carbasugar (5a-carba-R-D-galactopyranose) was isolated from a fermentation broth of Streptomyces sp. MA-4145. In the following decades, the chemistry and biology of carbasugars have been extensively studied. Most of these compounds show interesting biological properties, especially enzymatic inhibitory activities, and, in consequence, an important number of analogues have also been prepared in the search for improved biological activities. The aim of this review is to give coverage on the progress made in two important aspects of these compounds: the elucidation of their biosynthesis and the consideration of their biological properties, including the extensively studied carbapyranoses as well as the much less studied carbafuranoses.

How a diversity-oriented approach has inspired a new hypothesis for the gabosine biosynthetic pathway. A new synthesis of (+)-gabosine C

A new synthesis of (+)-gabosine C has been accomplished as part of a general diversity-oriented approach that also delivered the previously unknown (-)-4-epi-gabosine C. The identification of the unexpected intermediate (+)-8, together with the isolation of ketones 9 and 10 in previous investigations, prompted us to formulate a new hypothesis for the biosynthesis of gabosines, based on a keto-enol equilibrium cascade pathway starting from 2-epi-5-epi-valiolone, along which the necessary precursors for all the different types of gabosines are generated.

RETRACTED: Marine actinobacterial metabolites: current status and future perspectives

This article has been retracted: please see Elsevier Policy on Article Withdrawal (https://www.elsevier.com/about/our-business/policies/article-withdrawal). This article has been retracted at the request of the Editor. Authors and Editor agreed to retract this article because substantial parts of the text were copied from the following sources without proper attribution: Lam, K.S. (2006), Discovery of novel metabolites from marine actinomycetes. Current Opinion in Microbiology 9(3), pp. 245–251; Subramani, R., Aalbersberg, W. (2012), Marine actinomycetes: An ongoing source of novel bioactive metabolites. Microbiological Research 167(10), pp. 571–580; Dharmaraj, S. (2010), Marine Streptomyces as a novel source of bioactive substances. World Journal of Microbiology and Biotechnology 26(12), pp. 2123–2139. The authors apologize for this oversight and any inconvenience caused.

Marine actinomycetes: an ongoing source of novel bioactive metabolites

Actinomycetes are virtually unlimited sources of novel compounds with many therapeutic applications and hold a prominent position due to their diversity and proven ability to produce novel bioactive compounds. There are more than 22,000 known microbial secondary metabolites, 70% of which are produced by actinomycetes, 20% from fungi, 7% from Bacillus spp. and 1-2% by other bacteria. Among the actinomycetes, streptomycetes group are considered economically important because out of the approximately more than 10,000 known antibiotics, 50-55% are produced by this genus. The ecological role of actinomycetes in the marine ecosystem is largely neglected and various assumptions meant there was little incentive to isolate marine strains for search and discovery of new drugs. The search for and discovery of rare and new actinomycetes is of significant interest to drug discovery due to a growing need for the development of new and potent therapeutic agents. Modern molecular technologies are adding strength to the target-directed search for detection and isolation of bioactive actinomycetes, and continued development of improved cultivation methods and molecular technologies for accessing the marine environment promises to provide access to this significant new source of chemical diversity with novel/rare actinomycetes including new species of previously reported actinomycetes.

Polyoxygenated methyl cyclohexanoids from a terrestrial ampelomyces fungus

Seven structurally related new polyoxygenated methyl cyclohexanoids, ampelomins A-G (1-7), were isolated from the mycelial solid culture of a soil-derived Ampelomyces fungus. Their structures were determined by spectroscopic and chemical means. Ampelomins A (1), C (3), E (5), and G (7) exhibited weak activity against alpha-glucosidase with IC(50) values of 1.74-5.93 mM, and ampelomin A (1) showed moderate antibacterial activity with MIC(90) values ranging from 202.4 to 1015.9 microM. A plausible polyketide biogenetic pathway is postulated for these compounds.

Biosynthesis of the bicycloalternarenes, mixed terpenoids of Alternaria alternata

By incorporation of [2-13C]-mevalonate, [1-13C]-acetate and [1-13C]-glucose we could reveal that the phytopathogenic fungus Alternaria alternata biosynthesized the mixed terpenoids bicycloalternarenes via the classic mevalonate pathway. The polyketid pathway does not participate in the biosynthesis of bicycloalternarenes, because there is no incorporation of [13C]-acetate into the C-ring of these compounds. The labelling pattern in this nonterpenoid part of bicycloalternarenes after feeding with [1-13C]-glucose and [U-13C6]-glucose, respectively, allows the assumption that metabolites of the shikimate pathway are involved.