Isoswertisin flavones and other constituents fromPeperomia obtusifolia

Bioactive Phenolic Compounds from Peperomia obtusifolia

Peperomia obtusifolia (L.) A. Dietr., native to Middle America, is an ornamental plant also traditionally used for its mild antimicrobial properties. Chemical investigation on the leaves of P. obtusifolia resulted in the isolation of two previously undescribed compounds, named peperomic ester (1) and peperoside (2), together with five known compounds, viz. N-[2-(3,4-dihydroxyphenyl)ethyl]-3,4-dihydroxybenzamide (3), becatamide (4), peperobtusin A (5), peperomin B (6), and arabinothalictoside (7). The structures of these compounds were elucidated by 1D and 2D NMR techniques and HREIMS analyses. Compounds 1–7 were evaluated for their anthelmintic (against Caenorhabditis elegans), antifungal (against Botrytis cinerea, Septoria tritici and Phytophthora infestans), antibacterial (against Bacillus subtilis and Aliivibrio fischeri), and antiproliferative (against PC-3 and HT-29 human cancer cell lines) activities. The known peperobtusin A (5) was the most active compound against the PC-3 cancer cell line with IC₅₀ values of 25.6 µM and 36.0 µM in MTT and CV assays, respectively. This compound also induced 90% inhibition of bacterial growth of the Gram-positive B. subtilis at a concentration of 100 µM. In addition, compound 3 showed anti-oomycotic activity against P. infestans with an inhibition value of 56% by using a concentration of 125 µM. However, no anthelmintic activity was observed.

Fungal endophytes in Peperomia obtusifolia and their potential as inhibitors of chickpea fungal pathogens

Chickpea (Cicer arietinum L., Fabaceae) is the second most important legume after common bean (Phaseolus vulgaris L., Fabaceae) and third in production among the legumes grains worldwide. Ascochyta blight and Fusarium wilt are among the main fungal infections which cause the major losses of chickpea crop. In this work we report the phyto-pathogen controlling properties of 24 endophyte Phomopsis/Diaporthe isolates on the chickpea fungal pathogens Ascochyta rabiei, Fusarium oxysporum and Fusarium solani. The Phomopsis/Diaporthe strains were isolated amongst a total of 62 endophytic fungi from the aerial parts of the herbaceous perennial American plant Peperomia obtusifolia (Piperaceae) along with Fusarium, Septoria, Colletotrichum, Alternaria and Roussoella genera among others. Phomopsis/Diaporthe isolates were identified as Diaporthe infecunda (12 isolates), Diaporthe sackstoni (1 isolate), Diaporthe cf. brasiliensis (4 isolates) and Phomopsis cf. tuberivora (7 isolates). All the Phomopsis/Diaporthe strains antagonized A. rabiei strain AR2 with a mean of inhibition (% I) of 86.59 ± 1.49% in dual cultures. The metabolic characterization of the Phomopsis/Diaporthe strains showed groups in three clusters which were in agreement with the taxonomic identification. Bioautographic evaluation of organic extracts showed that those of D. cf. brasiliensis and D. infecunda were better as inhibitors. Strain Po 45 was one of the most active (cluster 1, 96.87% I), and its ethyl acetate extract inhibited A. rabiei growth in a bioautographic assay until at least 10 μg/mm applied showing a specific chromatographic band as the responsible of the A. rabiei inhibition.

Two new secondary metabolites isolated from Avena sativa L. (Oat) seedlings and their effects on osteoblast differentiation

Seedlings of natural crops are valuable sources of pharmacologically active phytochemicals. In this study, we aimed to identify new active secondary metabolites in Avena sativa L. (oat) seedlings. Two new compounds, avenafuranol (1) and diosgenoside (2), along with eight known compounds (3-10) were isolated from the A. sativa L. seedlings. Their chemical structures were elucidated via 1D and 2D NMR spectroscopy, high-resolution ESIMS, IR spectroscopy, optical rotation analysis, and comparisons with the reported literature. The effect of each isolated compound on alkaline phosphatase (ALP) activity for osteoblast differentiation induced by bone morphogenetic protein-2 (BMP-2) was investigated using the C2C12 immortal mouse myoblast cell line. Compounds 1, 4, 6, 8, and 9 induced dose-dependent increases in ALP expression relative to ALP expression in cells treated with only BMP-2, and no cytotoxicity was observed. These results suggest that A. sativa L. seedlings are a natural source of compounds that may be useful for preventing bone disorders.

Antibacterial activity of prenylated benzopyrans from Peperomia obtusifolia (Piperaceae)

Peperomia obtusifolia is a herbaceous perennial plant native to the Americas reported as a traditional medicine to treat snake bites and as a skin cleanser. The bioassay-guided fractionation of crude extracts from aerial parts of P. obtusifolia against a panel of clinically important fungi and bacteria, showed that hexane and dichloromethane extracts demonstrated selective bacterial inhibition, allowing the isolation of the known compounds peperobtusin A (1), and 3,4-dihydro-5-hydroxy-2,7-dimethyl-8-(3"-methyl-2"-butenyl)-2-(4'-methyl-1',3'-pentadienyl)-2H-1-benzopyran-6-carboxylic acid (2) from dichloromethane extract. Compound 2 was active against Gram-positive bacteria including community acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) isolates and an Enterococcus faecalis vancomycin-resistant strain, with minimal inhibitory concentration (MIC) values of 4 μg/mL (10.8 μM) and 8 μg/mL (21.6 μM) respectively. The interaction of compound 2 with the bacterial membrane was demonstrated by means of Zeta potential experiments on S. aureus, then confirming the membrane damage by fluorescent microscopy experiments.

Formation of a Methylenedioxy Bridge in (+)-Epipinoresinol by CYP81Q3 Corroborates with Diastereomeric Specialization in Sesame Lignans

Plant specialized metabolites are often found as lineage-specific diastereomeric isomers. For example, Sesamum alatum accumulates the specialized metabolite (+)-2-episesalatin, a furofuran-type lignan with a characteristic diastereomeric configuration rarely found in other Sesamum spp. However, little is known regarding how diastereomeric specificity in lignan biosynthesis is implemented in planta. Here, we show that S. alatum CYP81Q3, a P450 orthologous to S. indicum CYP81Q1, specifically catalyzes methylenedioxy bridge (MDB) formation in (+)-epipinoresinol to produce (+)-pluviatilol. Both (+)-epipinoresinol and (+)-pluviatilol are putative intermediates of (+)-2-episesalatin based on their diastereomeric configurations. On the other hand, CYP81Q3 accepts neither (+)- nor (-)-pinoresinol as a substrate. This diastereomeric selectivity of CYP81Q3 is in clear contrast to that of CYP81Q1, which specifically converts (+)-pinoresinol to (+)-sesamin via (+)-piperitol by the sequential formation of two MDBs but does not accept (+)-epipinoresinol as a substrate. Moreover, (+)-pinoresinol does not interfere with the conversion of (+)-epipinoresinol to (+)-pluviatilol by CYP81Q3. Amino acid substitution and CO difference spectral analyses show that polymorphic residues between CYP81Q1 and CYP81Q3 proximal to their putative substrate pockets are crucial for the functional diversity and stability of these two enzymes. Our data provide clues to understanding how the lineage-specific functional differentiation of respective biosynthetic enzymes substantiates the stereoisomeric diversity of lignan structures.

Comparative metabolomic responses to gibberellic acid and 6-benzylaminopurine in Cunila menthoides Benth. (Lamiaceae): a contribution to understand the metabolic pathways

Gibberellic acid elicited synthesis of many phenols from different classes and enhanced production of sesquiterpenoids, polyterpenoids, steroids and monoterpenoids compared to control and 6-benzylaminopurine. Little is known about the effects of 6-benzylaminopurine (BA) and gibberellic acid (GA3) on the synthesis of secondary metabolites in species of Lamiaceae. In this study, for the first time, the profile of secondary metabolites in plantlets of Cunila menthoides was characterized, using UPLC-ESI-Qq-oaTOF-MS. Ninety metabolites were identified, including polyphenols and terpenes. BA down-regulated most of the identified molecules in relation to GA3 and MS0 (control). The results showed that GA3 elicited synthesis of many phenols from different classes, and seemed to play a major role in the shikimate pathway in relation to BA. GA3 enhanced production of sesquiterpenoids, polyterpenoids, steroids and monoterpenoids compared to MS0 and BA, and also seemed to positively influence the MEP/DOXP and MVA pathways. These data show the most comprehensive metabolomic profile of Cunila menthoides to date, and the effects of BA and GA3 on the synthesis of secondary metabolites, modulating quantitative aspects of metabolism in Lamiaceae.

The Combined Use of Proteomics and Transcriptomics Reveals a Complex Secondary Metabolite Network in Peperomia obtusifolia

Peperomia obtusifolia, an ornamental plant from the Piperaceae family, accumulates a series of secondary metabolites with interesting biological properties. From a biosynthesis standpoint, this species produces several benzopyrans derived from orsellinic acid, which is a polyketide typically found in fungi. Additionally, the chiral benzopyrans were reported as racemic and/or as diastereomeric mixtures, which raises questions about the level of enzymatic control in the cyclization step for the formation of the 3,4-dihydro-2H-pyran moiety. Therefore, this article describes the use of shotgun proteomic and transcriptome studies as well as phytochemical profiling for the characterization of the main biosynthesis pathways active in P. obtusifolia. This combined approach resulted in the identification of a series of proteins involved in its secondary metabolism, including tocopherol cyclase and prenyltransferases. The activity of these enzymes was supported by the phytochemical profiling performed in different organs of P. obtusifolia. However, the polyketide synthases possibly involved in the production of orsellinic acid could not be identified, suggesting that orsellinic acid may be produced by endophytes intimately associated with the plant.