Aquayamycin

Total syntheses of aquayamycin (3) and a number of analogues of angucycline antitumor antibiotic derhodinosylurdamycin A bearing various 2-deoxy sugar subunits (4-7) have been achieved. These molecules (3-7) were synthesized based on a convergent strategy for the synthesis of derhodinosylurdamycin A (2) previously reported from our group. In particular, our recently developed mild cationic gold-catalyzed glycosylation with S-but-3-ynyl thioglycoside donors was employed for the synthesis of analogues (6 and 7) bearing disaccharide subunits containing α-l-olivoside and α-l-olioside moiety, respectively. Aquayamycin (3), analogues (4-7), and our previously synthesized derhodinosylurdamycin A (2) were then submitted to the Development Therapeutics Program of the National Cancer Institute of National Institutes of Health for the NCI-60 Human Tumor Cell Lines Screening using standard protocols. It was found that derhodinosylurdamycin A (2), aquayamycin (3), and three other analogues (5-7) bearing sugar subunits did not show significant antiproliferative activity against those cancer cell lines. Interestingly, analogue (4) bearing no sugar subunit demonstrates good potential for growth inhibition and cytotoxic activity against a variety of human cancer cell lines.

Actinobacteria are a rich source of bioactive molecules, and genome sequencing has shown that the vast majority of their biosynthetic potential has yet to be explored. However, many of their biosynthetic gene clusters (BGCs) are poorly expressed in the laboratory, which prevents discovery of their cognate natural products. To exploit their full biosynthetic potential, better understanding of the signals that promote the expression of BGCs is needed. Here, we show that the human stress hormone epinephrine (adrenaline) elicits siderophore production by Actinobacteria. Catechol was established as the likely eliciting moiety, since similar responses were seen for catechol and for the catechol-containing molecules dopamine and catechin but not for related molecules. Exploration of the catechol-responsive strain Streptomyces sp. MBT84 using mass spectral networking revealed elicitation of a BGC that produces the angucycline glycosides aquayamycin, urdamycinone B and galtamycin C. Heterologous expression of the catechol-cleaving enzymes catechol 1,2-dioxygenase or catechol 2,3-dioxygenase counteracted the eliciting effect of catechol. Thus, our work identifies the ubiquitous catechol moiety as a novel elicitor of the expression of BGCs for specialized metabolites.

Natural products produced by bacteria found in unusual and poorly studied ecosystems, such as Lake Baikal, represent a promising source of new valuable drug leads. Here we report the isolation of a new Streptomyces sp. strain IB201691-2A from the Lake Baikal endemic mollusk Benedictia baicalensis. In the course of an activity guided screening three new angucyclines, named baikalomycins A-C, were isolated and characterized, highlighting the potential of poorly investigated ecological niches. Besides that, the strain was found to accumulate large quantities of rabelomycin and 5-hydroxy-rabelomycin, known shunt products in angucyclines biosynthesis. Baikalomycins A-C demonstrated varying degrees of anticancer activity. Rabelomycin and 5-hydroxy-rabelomycin further demonstrated antiproliferative activities. The structure elucidation showed that baikalomycin A is a modified aquayamycin with β-d-amicetose and two additional hydroxyl groups at unusual positions (6a and 12a) of aglycone. Baikalomycins B and C have alternating second sugars attached, α-l-amicetose and α-l-aculose, respectively. The gene cluster for baikalomycins biosynthesis was identified by genome mining, cloned using a transformation-associated recombination technique and successfully expressed in S. albus J1074. It contains a typical set of genes responsible for an angucycline core assembly, all necessary genes for the deoxy sugars biosynthesis, and three genes coding for the glycosyltransferase enzymes. Heterologous expression and deletion experiments allowed to assign the function of glycosyltransferases involved in the decoration of baikalomycins aglycone.