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Two new cyclic lipopeptides (3 and 4) were isolated from the culture filtrate of Bacillus amyloliquefaciens strain SD-32, together with two known metabolites, iso-C15 and iso-C16 bacillomycin D (1 and 2). Spectroscopic and chemical analyses identified the structures of the new compounds 3 and 4 as anteiso-C17 bacillomycin D, cyclic (l-Asn-d-Tyr-d-Asn-l-Pro-l-Glu-d-Ser-l-Thr-3-amino-14-methylhexadecanoic acid) and iso-C17 bacillomycin D, cyclic (l-Asn-d-Tyr-d-Asn-l-Pro-l-Glu-d-Ser-l-Thr-3-amino-15-methylhexadecanoic acid), respectively. The absolute configuration of C-3 in the β-amino fatty acid was determined to be R on the basis of the CD spectrum of its dinitrophenyl-p-methoxyaniline derivative. The activities of compounds 1-4 were evaluated against 13 plant pathogens: the activities of anteiso- and iso-C17 bacillomycin D (3 and 4) were almost the same and stronger than those of iso-C15 and iso-C16 bacillomycin D (1 and 2); iso-C15 bacillomycin D (1) was weakest. Compounds 2-4 inhibited the growth of all fungi tested; however, Pythium aphanidermatum was not inhibited at all by any of the compounds. Furthermore, compounds 1-4 at concentrations of 80, 40, 30, and 30 μM, respectively, inhibited completely the Botrytis cinerea infection in cucumber leaf.

This study demonstrates that prumycin is a major factor in SD-32's suppression of cucumber powdery mildew disease. Our findings shed light for the first time on prumycin's role in biocontrol by Bacillus against this disease. © 2017 Society of Chemical Industry.

We previously reported that Bacillus amyloliquefaciens biocontrol strain SD-32 produces powerful antifungal lipopeptides, C17 bacillomycin D homologues. In the course of the investigation we found that the antifungal activity of the culture supernatant of this bacterium was not ascribed exclusively to bacillomycin D. We attempted to identify metabolites other than bacillomycin D to gain insight into the mechanism for the biocontrol by this bacterium. After purifying the fractions of the culture supernatant exhibiting synergistic activity with bacillomycin D, we isolated two new cyclic lipodepsipeptides, anteiso-C13 and iso-C13 [Ile(7)]surfactins, together with three known [Ile(7)]surfactins. Interestingly, [Ile(7)]surfactins showed synergistic activities with bacillomycin D to gray mold disease on cucumber leaves but not to Botrytis cinerea itself in vitro, suggesting that the synergistic effects might be on infection processes of the fungus. Actually, we observed that they did not show synergistic actions on conidial germination or mycelial growth of B. cinerea on the leaves.

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The reaction of 4-hydroxy-2H-pyran-2-one derivatives (I), ( l l ) , and (17) with a range of alkenes or phenylacetylene in acetonitrile containing cerium(1V) ammonium nitrate (CAN) afforded the corresponding furo [3,2clpyranone (4,8, 13, 15, and 18) and/or furo[2,3-blpyranone derivatives (6, 10, 1 4 , 16, and 19). Similar treatment of 4-hydroxy-I-methylquinolin-2(1H)-one (2) with alkenes or phenylacetylene in the presence of CAN gave furo[3,2-clquinolin-4(5H)-one derivatives (5) and (9).As part of a program aimed at developing new methods for the preparation of furan-fused aromatic] and heterocyclic compounds,2 we recently reportedla on a one-step construction of benzofurandione and naphthofurandione derivatives by a [3+2] type cycloaddition of 2-hydroxy-1.4-benzoquinones and 2hydroxy-l,4-naphthoquinones with alkenes (or phenylacetylene) mediated by cerium(1V) ammonium nitrate (CAN).3 We were interested in investigating the possibility of extending this CAN-mediated cycloaddition to enolizable heterocyclic p-dicarbonyl compounds.4 We first examined the reactions using 4-hydroxy-2Hbenzo-I-pyran-2-one (4-hydroxycoumarin) (1)s and 4-hydroxy-I-methylquinolin-2(1H)-one (2).5. 6 We found that the reaction of 1 with alkenes (3) or phenylacetylene (7) in the presence of CAN afforded the corresponding 4H-furo[3,2-c]benzo[l]pyran-4-one (4 or 8) andlor 4H-furo[2,3-b]henzo[l]pyran-4-onederivatives (6 or 10) and that the reaction of 2 with 3 or 7 gave furo[3,2-clquinolin-4(5H)-one derivatives ( 5 ) or (9).7 In further investigation we found that 4-hydroxy-6-methyl-2H-pyran-2-one (11)s or Ihydroxy-3H-naphtho[2,l-b]pyran-3-one (17) gave 4H-furo[3,2-clpyran-4-one (13 and 15) and(or) 4Hfuro[2,3-blpyran-4-one derivatives (14 and 16), or 4Hnnaphtho[2,1-b]furo[2,3-dlpyran-4-one (18) and 1 IH-naphtho[2,I-b]furo[3,2-elpyran-I I-one derivatives (19). respectively.8.9 A number of efficient procedures for achieving the construction of above-mentioned furopyranonel(1 and furoquinolinone~ I

The reaction of 2-hydroxy-1,4-naphthoquinones with enamines, derived from ketones, in refluxing toluene afforded the corresponding 2,3-disubstituted naphtho [2,3-b ]furan-4,9-dione derivatives in moderate to good yields.The synthesis of furonaphthoquinones is of major importance in quinonoid synthesis; some of them have been found in nature. 1 A number of elegant methods now exist to prepare this class of compounds. 2 Most of them, however, rely on multistep conversions. 3 Kakisawa and co-workers have reported that 2-acetoxy-1,4-naphthoquinones can be converted to 3-methylnaphtho[2,3-b ]-furan-4,9-diones in one pot via their treatment with an enamine derived from propionaldehyde. 4 This is a rare example of quinone derivatives undergoing heterocycle construction reactions with enamines without losing the quinone skeleton, although a number of procedures for the synthesis of heterocyclic compounds utilizing the reactions of quinones with enamines 5 have been described in the literature since the first by Nenitzescu in 1929. 6 We have now found that 2,3-disubstituted naphtho[2,3-b ]furan-4,9-diones 3 can be directly obtained by the reactions of 2-hydroxy-1,4-naphthoquinones 1 with enamines 2 , derived from ketones, in toluene at reflux temperature (Scheme 1).The furoquinones 3 were produced without any formation of the corresponding o -quinone derivatives. The results obtained by using series of 1 and 2 are summarized in the Table. The progress of the reactions could be readily monitored by TLC on silica gel. These reactions did not take place to any appreciable extent at room temperature. For example, carrying out the reaction of 2-hydroxy-1,4-naphthoquinone (1a) with 1-pyrrolidinocyclohexene (2a) at room temperature for 3 days resulted in only a 3% yield of the furonaphthoquinone 3a . A stable enamine, such as 1-pyrrolidino-3,4-dihydronaphthalene (2e) , was also found to be effective in the present transformation, and the dinaphthofurandione 3e was obtained but in somewhat decreased yield (entry 5). While most of the reactions were complete within 7 to 10 hours to give the products in fair-to-good yields, the reactions of the methoxylated hydroxynaphthoquinones 1b and 1c with 2a proceeded sluggishly. However, acceptable yields of the expected furoquinones were obtained with longer reaction times (entries 6 and 7, respectively). The lower reactivity of these quinones can be attributed to the methoxy substituents attached to the benzene nucleus, which cause them to be unsusceptible to reaction with nucleophiles.