Note pubs.acs.org/jnp Antibiotic and Antimalarial Quinones from Fungus-Growing Ant- Associated Pseudonocardia sp. Gavin Carr,† Emily R. Derbyshire,† Eric Caldera,‡ Cameron R. Currie,‡ and Jon Clardy*,† †Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, Massachusetts 02115, United States ‡Department of Bacteriology, University of Wisconsin−Madison, Madison, Wisconsin 53706, United States *S Supporting Information ABSTRACT: Three new members of the angucycline class of antibiotics, pseudonocardones A−C (1−3), along with the known antibiotics 6-deoxy-8-O-methylrabelomycin (4) and X- 14881 E (5) have been isolated from the culture of a Pseudonocardia strain associated with the fungus-growing ant Apterostigma dentigerum. Compounds 4 and 5 showed antibiotic activity against Bacillus subtilis 3610 and liver-stage Plasmodium berghei, while 1−3 were inactive or only weakly active in a variety of biological assays. Compound 5 also showed moderate cytotoxicity against HepG2 cells. B growing ants1 and produce antibiotics that presumptively acteria of the genus Pseudonocardia associate with fungus- play a role in suppressing fungal pathogens in ants’ gardens.2,3 While Pseudonocardia belongs to the Actinomycetales, which are well known for their remarkable ability to produce bioactive secondary metabolites, relatively few natural products have been described from Pseudonocardia spp. Antibiotics discovered from Pseudonocardia spp. include dentigerumycin,3 pseudono- cardians A and B,4 phenazostatin D,5 and NPP.6 Of these, only dentigerumycin was discovered from a Pseudonocardia strain associated with fungus-growing ants, and these symbionts likely have many more undiscovered natural products. As part of our ongoing eﬀort to explore natural products from bacterial symbionts,3,7−9 we have investigated the natural products from Pseudonocardia sp. EC080529-01, isolated from the cuticle of the fungus-growing ant Apterostigma dentigerum.10 This strain produces three new members of the angucycline family of antibiotics,11 pseudonocardones A (1), B (2), and C (3), along with the known antibiotics 6-deoxy-8-O-methylrabelomycin (4)12 and X-14881 E (5).13 Pseudonocardia sp. EC080529-01 was grown on solid ISP-2 medium, and the agar was extracted with EtOAc followed by MeOH. HPLC-MS analysis of the EtOAc extract revealed two peaks with interesting UV spectra (λmax at 381 and 410 nm, respectively). HPLC-MS analysis of the MeOH extract revealed three additional polar peaks with λmax at 348 nm, 388, and 409 nm, respectively. Production cultures of Pseudonocardia sp. EC080529-01 were grown on solid ISP-2 medium and extracted with EtOAc followed by MeOH. The EtOAc extract was puriﬁed (see Experimental Section) to give 6-deoxy-8-O- methylrabelomycin (4, 8.3 mg) and X-14881 E (5, 3.5 mg). The MeOH extract was puriﬁed (see Experimental Section) to give pseudonocardones A (1, 2.0 mg), B (2, 0.9 mg), and C (3, 1.8 mg). The known compounds 4 and 5 were identiﬁed by 1D and 2D NMR spectroscopy, and their structures were conﬁrmed by comparison of their spectroscopic data with the literature values.12,13 Pseudonocardone A (1) gave a peak in the HRESI(+) MS consistent with a molecular formula of C26H24O10. The NMR data (Figures 1 and 2 and Table 1) obtained for 1 indicated that it was related to the angucycline family of antibiotics and that it was similar in structure to 5. The peak in the UV spectrum of 5 at λmax = 410 nm had shifted to λmax = 348 nm. While compound 5 showed two carbon resonances typical of a quinone (δC 191.3 and 182.0), compound 1 showed only one carbon resonance in this range (δC 186.0). Instead, compound 1 showed a signal for an oxygenated methine resonance (δC 66.5; δH 6.93). This methine resonance showed HMBC correlations to C-6a (δC 132.5), C-7a (δC 120.8), C-11 (δC 123.8), C-11a (δC 147.7), C-12a (δC 139.6), and C-12b Received: May 30, 2012 Published: October 1, 2012 © 2012 American Chemical Society and American Society of Pharmacognosy 1806 dx.doi.org/10.1021/np300380t | J. Nat. Prod. 2012, 75, 1806−1809