The generation of natural product libraries containing column fractions, each with only a few small molecules, using a high-throughput, automated fractionation system, has made it possible to implement an improved dereplication strategy for selection and prioritization of leads in a natural product discovery program. Analysis of databased UPLC-MS-ELSD-PDA information of three leads from a biological screen employing the ependymoma cell line EphB2-EPD generated details on the possible structures of active compounds present. The procedure allows the rapid identification of known compounds and guides the isolation of unknown compounds of interest. Three previously known flavanone-type compounds homoeriodictyol (1), hesperetin (2), and sterubin (3) were identified in a selected fraction derived from the leaves of Eriodictyon angustifolium. The lignan compound deoxypodophyllotoxin (8) was confirmed to be an active constituent in two lead fractions derived from the bark and leaves of Thuja occidentalis. In addition, two new but inactive labdane-type diterpenoids with an uncommon triol side chain were also identified as coexisting with deoxypodophyllotoxin in a lead fraction from the bark of T. occidentalis. Both diterpenoids were isolated in acetylated form, and their structures were determined as 14S,15-diacetoxy-13R-hydroxy-labd-8(17)-en-19-oic acid (9) and 14R,15-diacetoxy-13S-hydroxy-labd-8(17)-en-19-oic acid (10), respectively, by spectroscopic data interpretation and X-ray crystallography. This work demonstrates that a UPLC-MS-ELSD-PDA database produced during fractionation may be used a powerful dereplication tool to facilitate compound identification from chromatographically tractable small molecule natural product libraries.

Miltefosine is an alkylphosphocholine that shows broad-spectrum in vitro antifungal activities and limited in vivo efficacy in mouse models of cryptococcosis. To further explore the potential of this class of compounds for the treatment of systemic mycoses, nine analogs (3a–3i) were synthesized by modifying the choline structural moiety and the alkyl chain length of miltefosine. In vitro testing of these compounds against the opportunistic fungal pathogens Candida albicans, Candida glabrata, Candida krusei, Aspergillus fumigatus, and Cryptococcus neoformans revealed that N-benzyl-N,N-dimethyl-2-{[(hexadecyloxy)hydroxyphosphinyl]oxy}ethanaminium inner salt (3a), N,N-dimethyl-N-(4-nitrobenzyl)-2-{[(hexadecyloxy)hydroxyphosphinyl]oxy}ethanaminium inner salt (3d), and N-(4-methoxybenzyl)-N,N-dimethyl-2-{[(hexadecyloxy)hydroxyphosphinyl]oxy}ethanaminium inner salt (3e) exhibited minimum inhibitory concentrations (MIC) of 2.5–5.0 μg/mL against all tested pathogens, when compared to miltefosine with MICs of 2.5–3.3 μg/mL. Compound 3a showed low in vitro cytotoxicity against three mammalian cell lines similar to miltefosine. In vivo testing of 3a and miltefosine against C. albicans in a mouse model of systemic infection did not demonstrate efficacy. The results of this study indicate that further investigation will be required to determine the potential usefulness of the alkylphosphocholines in the treatment of invasive fungal infections.

Bioassay-guided fractionation of the organic extracts of a Bacillus amyloliquefaciens strain (AP183) led to the discovery of a new macrocyclic polyene antibiotic, bacillusin A (1). Its structure was assigned by interpretation of NMR and MS spectroscopic data as a novel macrodiolide composed of dimeric 4-hydroxy-2-methoxy-6-alkenylbenzoic acid lactones with conjugated pentaene-hexahydroxy polyketide chains. Compound 1 showed potent antibacterial activities against methicillin-resistant Staphylococcus aureus and vancomycin-resistant Enterococcus faecium with minimum inhibitory concentrations in a range of 0.6 to 1.2 μg/mL. The biosynthetic significance of this unique class of antibiotic compounds is briefly discussed.

Fourteen compounds including vanicoside B (1), vanicoside F (2), vanicoside E (3) and 5,6-dehydrokawain (4), aniba-dimer-A (5), 6,6'-((1α,2α,3β,4β)-2,4-diphenylcyclobutane-1,3-diyl)bis(4-methoxy-2H-pyran-2-one) (6), (+)-ketopinoresinol (7), isorhamnetin (8), 3,7-dihydroxy-5,6-dimethoxy-flavone (9), isalpinin (10), cardamomin (11), pinosylvin (12), 2-desoxy-4-epi-pulchellin (13) and β-sitosterol (14) were isolated from dichloromethane-soluble portion of Polygonum hydropiper. By using Alamar blue assay, compounds 2, 7, 8, 11 and 12 were found to be active against Trypanosoma brucei with IC values in the range of 0.49-7.77 μg/mL. Cardamomin (11) had most significant activity against T. brucei with IC/IC values of 0.49/0.81 μg/mL compared to the positive control DFMO (IC/IC: 3.02/8.05 μg/mL). Furthermore, in antimalarial, antimicrobial, anti-inflammatory, PPAR and cytotoxic assays, some compounds have demonstrated moderate inhibitory potentials.

Thirty-three natural-product-based acylphloroglucinol derivatives were synthesized to identify antifungal compounds against Cryptococcus spp. that cause the life-threatening disseminated cryptococcosis. In vitro antifungal testing showed that 17 compounds were active against C. neoformans ATCC 90113, C. neoformans H99, and C. gattii ATCC 32609, with minimum inhibitory concentrations (MICs) in the range 1.0-16.7 μg/mL. Analysis of the structure and antifungal activity of these compounds indicated that the 2,4-diacyl- and 2-acyl-4-alkylphloroglucinols were more active than O-alkyl-acylphloroglucinols. The most promising compound found was 2-methyl-1-(2,4,6-trihydroxy-3-(4-isopropylbenzyl)phenyl)propan-1-one (11j), which exhibited potent antifungal activity (MICs, 1.5-2.1 μg/mL) and low cytotoxicity against the mammalian Vero and LLC-PK1 cell lines (IC50 values >50 μg/mL). This compound may serve as a template for further synthesis of new analogues with improved antifungal activity. The findings of the present work may contribute to future antifungal discovery toward pharmaceutical development of new treatments for cryptococcosis.

A functional metagenomic approach identified novel and diverse soil-derived DNAs encoding inhibitors to methicillin-resistant Staphylococcus aureus (MRSA). A metagenomic DNA soil library containing 19 200 recombinant Escherichia coli BAC clones with 100 Kb average insert size was screened for antibiotic activity. Twenty-seven clones inhibited MRSA, seven of which were found by LC-MS to possess modified chloramphenicol ( Cm) derivatives, including three new compounds whose structures were established as 1-acetyl-3-propanoylchloramphenicol, 1-acetyl-3-butanoylchloramphenicol, and 3-butanoyl-1-propanoylchloramphenicol. Cm was used as the selectable antibiotic for cloning, suggesting that heterologously expressed enzymes resulted in derivatization of Cm into new chemical entities with biological activity. An esterase was found to be responsible for the enzymatic regeneration of Cm, and the gene trfA responsible for plasmid copy induction was found to be responsible for inducing antibacterial activity in some clones. Six additional acylchloramphenicols were synthesized for structure and antibacterial activity relationship studies, with 1- p-nitrobenzoylchloramphenicol the most active against Mycobacterium intracellulare and Mycobacterium tuberculosis, with MICs of 12.5 and 50.0 μg/mL, respectively.

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Psorothatins A-C (1-3), three antibacterial prenylated acylphloroglucinol derivatives, were isolated from the native American plant Psorothamnus fremontii. They feature an unusual α,β-epoxyketone functionality and a β-hydroxy-α,β-unsaturated ketone structural moiety. The latter forms a pseudo-six-membered heterocyclic ring due to strong intramolecular hydrogen bonding, as indicated by the long-range proton-carbon correlations in the NMR experiments. Psorothatin C (3) was the most active compound against methicillin-resistant Staphylococcus aureus and vancomycin-resistant Enterococcus faecium, with IC50 values in the range 1.4-8.8 μg/mL. The first total synthesis of 3 described herein permits future access to structural analogues with potentially improved antibacterial activities.