Spirotoamides A and B, novel 6,6-spiroacetal polyketides isolated from a microbial metabolite fraction library

Abstract

Two new 6,6-spiroacetal polyketides, spirotoamides A (1) and B (2), were isolated from a microbial metabolite fraction library of Streptomyces griseochromogenes JC82-1223 by screening of structurally unique compounds based on a search of spectral database. The fraction library was constructed using a systematic separation method to efficiently discover new metabolites from microbial sources such as actinomycetes and fungi. The structures of 1 and 2 were elucidated by 2D-NMR and mass spectrometric measurements. They belong to a class of polyketides, and contain a 6,6-spiroacetal core structure and a carboxamide group. The biosynthetic pathway of 1 and 2 is discussed in the text. Keywords: fraction library; microbial metabolite; spiroacetal polyketide; Streptomyces griseochromogenes; structure elucidation INTRODUCTION Microorganisms, such as actinomycetes and fungi, have a tremendous capacity to produce structurally diverse metabolites 1 with disparate activities, rendering them a significant source of pharmaceutical leads and therapeutic agents. 2,3 They are also used as potential bioprobes for chemical biology studies. 4,5 Many secondary metabolites have been reported, but not all have been isolated, nor have their wide-ranging physicochemical properties and low abundance been examined with regard to their potentially useful activities. Thus, we constructed a microbial metabolite fraction library by systematic separation with a spectral database, based on photodiode-array detector attached LC/MS analysis to discover structurally unique metabolites efficiently and rapidly. We discovered and isolated verticilactam 6 from S. spiroveticillatus JC-8444, a tautomycin producer, 7-9 and the new fraquinocins I and J 10 and 6-dimethylalylindole-3-carbaldehyde 11 from S. reveromyceticus SN-593, a reveromycin producer 12 by our methodology constructing the fraction library. Also, Bugni et al. 13 reported a marine natural products library by HPLC-MS fractionation for rapid drug discovery. These reports have demonstrated the advantage of fraction libraries in isolating and investigating the activities of natural products.Our microbial fraction library was developed on basic chromatographic techniques, comprizing two-step separation by middlepressure liquid chromatography (MPLC) and C 18 -HPLC, yielding 300-400 fractions from a single microbial strain with reproducibility. In addition to many known compounds, the fractions, which contain unidentified minor components, might contain valuable compounds

RK-270A−C, new oxindole derivatives isolated from a microbial metabolites fraction library of Streptomyces sp. RK85-270

“…2 To obtain such valuable metabolites efficiently we have constructed a microbial metabolites fraction library and a spectral database based on the photodiode array detector attached LC/MS analysis. 3,4 Through our methodology, we have identified several structurally unique metabolites, verticilactam, 5 spirotoamides A and B, 6 pyrrolizilactone, 7 fraquinocins I and J 8 and 6-dimethylallylindole (DMAI)-3-carbaldehyde. 9 Moreover, we recently reported the advanced metabolite database Natural Products Plot (NPPlot) and discovery of new quinomycins, RK-1355A and B by the NPPlot search.…”

“…RK85-270, which was isolated from a soil sample collected in Java, Indonesia in 1985, was prepared from 30 l of culture broth following the scheme as described in the previous paper. [3][4][5][6] On screening for structurally unique secondary metabolites using the database, we identified three unknown peaks with identical UV, which showed characteristic UV absorption with around 260, 265 and 300 nm indicating an indole chromophore with extended conjugation. They also showed quasimolecular ion peaks at 242, 276 and 271 [M+H] + , respectively.…”

“…Compound 1 was obtained as an orange amorphous powder, and its molecular formula was determined to be C 6.74 (1H, dd, J = 8.0, 1.1 Hz) and 6.60 (1H, d, J = 1.1 Hz)) suggesting the presence of a trisubstituted benzene ring, which was supposed to be a part of an indole skeleton. The 1 H and 13 C NMR data in conjunction with the HSQC data suggested the presence of 16 carbons, comprising four methyls, one methylene, four methins and seven quaternary carbons, which included an amide carbonyl signal at δ C 168.8.…”

Streptospirodienoic acids A and B, 6,6-spiroketal polyketides from Streptomyces sp.

“…The 6,6-spiroketal core structure may be constructed by cyclization of epoxide/ketone intermediate (Scheme 1) or through dehydrative cyclization. [6][7][8] It is very interesting that streptospirodienoic acids may have close relationship with bafilomycin A 9 , a 16-membered macrolide isolated from the broth of Streptomyces griseus, from the view of biogenetic pathway. Both of them were derived from the polyketide pathway and the starter group and extend units of them might be similar.…”

Pyrrolizilactone, a new pyrrolizidinone metabolite produced by a fungus

“…4,5 To search for and discover such structurally unique metabolites efficiently and rapidly, we have constructed a microbial metabolite fraction library with a spectral database on the basis of photodiode array detectorattached LC/MS analysis. 6,7 Through our methodology for the construction of this fraction library, we discovered and identified a 16-membered macrolactam with an unusual b-keto-amide moiety, verticilactam, 8 6,6-spiroacetal polyketide, spirotoamides, A and B, 9 the new fraquinocins, I and J, 10 and 6-dimethylallylindole-3carbaldehyde. 11 These results demonstrate the advantage of the fraction library in isolating novel metabolites from natural sources.…”