Unusual chromenes from Peperomia blanda

Chromene and chromone derivatives as liver X receptors modulators from a marine-derived Pestalotiopsis neglecta fungus

Four new chromene derivatives, pestalotiochromenoic acids A - D (1, 2, 4, and 5), and two new chromone derivatives, pestalotiochromones A and B (6 and 7), were obtained from the marine alga-derived fungus Pestalotiopsis neglecta SCSIO41403, as well as a reported derivate named piperochromenoic acid (3) with its configuration determined for the first time. Their structures were determined by detailed nuclear magnetic resonance (NMR) and mass spectroscopic analyses, while the absolute configurations were established by theoretical NMR and electronic circular dichroism (ECD) calculation, including Mo₂(OAc)₄-induced ECD experiments. Those chromene and chromone derivatives displayed weak cytotoxicity, but showed obvious liver X receptors (LXRs) modulatory activities, by in vitro tests on the expression of LXRα, LXRβ and theirtarget gene ABCA1, as well as in silico docking analysis. Moreover, the high binding affinities between pestalotiochromone A (6) and LXRα, revealed by surface plasmon resonance (SPR) with the dissociation equilibrium constant (K_D) value of 6.2 μM, demonstrated 6 could act as a new potential LXR agonist.

Non-Clinical Studies for Evaluation of 8-C-Rhamnosyl Apigenin Purified from Peperomia obtusifolia against Acute Edema

Compound 8-C-rhamnosyl apigenin (8CR) induced a moderate reduction in the enzymatic activity of secretory phospholipase A2 (sPLA2) from Crotalus durissus terrificus and cytosolic phospholipase A2 (cPLA2), but the compound also significantly inhibited the enzymatic activity of the enzyme cyclooxygenase. In vitro assays showed that the compound induced a slight change in the secondary structure of sPLA2 from Crotalus durissus terrificus snake venom. In vivo assays were divided into two steps. In the first step, the 8CR compound was administered by intraperitoneal injections 30 min prior to administration of sPLA2. In this condition, 8CR inhibited edema and myonecrosis induced by the sPLA2 activity of Crotalus durissus terrificus in a dose-dependent manner by decreasing interleukin-1β (IL-1β), tumor necrosis factor α (TNF-α), prostaglandin E2 (PGE2), and lipid peroxidation. This has been demonstrated by monitoring the levels of malondialdehyde (MDA) in rat paws after the course of edema induced by sPLA2. These results, for the first time, show that sPLA2 of Crotalus durissus terrificus venom induces massive muscle damage, as well as significant edema by mobilization of cyclooxygenase enzymes. Additionally, its pharmacological activity involves increased lipid peroxidation as well as TNF-α and IL-1β production. Previous administration by the peritoneal route has shown that dose-dependent 8CR significantly decreases the enzymatic activity of cyclooxygenase enzymes. This resulted in a decrease of the amount of bioactive lipids involved in inflammation; it also promoted a significant cellular protection against lipid peroxidation. In vivo experiments performed with 8CR at a concentration adjusted to 200 μg (8 mg/kg) of intraperitoneal injection 15 min after sPLA2 injection significantly reduced sPLA2 edema and the myotoxic effect induced by sPLA2 through the decrease in the enzymatic activity of cPLA2, cyclooxygenase, and a massive reduction of lipid peroxidation. These results clearly show that 8CR is a potent anti-inflammatory that inhibits cyclooxygenase-2 (COX-2), and it may modulate the enzymatic activity of sPLA2 and cPLA2. In addition, it was shown that Crotalus durissus terrificus sPLA2 increases cell oxidative stress during edema and myonecrosis, and the antioxidant properties of the polyphenolic compound may be significant in mitigating the pharmacological effect induced by sPLA2 and other snake venom toxins.

Efficient catalyst for tandem solvent free enantioselective Knoevenagel-formal [3+3] cycloaddition and Knoevenagel-hetero-Diels–Alder reactions

Tandem Knoevenagel-cycloaddition reactions forming bicyclic tetrahydro-2H-chromen-5(6H)-ones and tricyclic octahydro-2H-benzo[c]-chromen-1(6H)-ones are achieved with up to 98.8% ee in the presence of chiral LBA and titanium-isopropoxy-(S)-BINOLate.

3-Ishwarone, a rare ishwarane sesquiterpene from Peperomia scandens Ruiz & Pavon: structural elucidation through a joint experimental and theoretical study

3-Ishwarone, (1), a sesquiterpene with a rare ishwarane skeleton, was isolated from Peperomia scandens Ruiz & Pavon (Piperaceae). Its structure was unambiguously determined by 1D- and 2D-NMR and infrared analyses, as well as by comparative theoretical studies which involved calculations of 13C-NMR chemical shifts, using the Density Functional Theory (DFT) with the mPW1PW91 hybrid functional and Pople's 6-31G(d) basis set, and of vibrational frequencies, using the B3LYP hybrid functional and triple ζ Dunning's correlation consistent basis set (cc-pVTZ), of (1) and three of its possible diastereomers, compounds 2-4.

Absolute configuration and selective trypanocidal activity of gaudichaudianic acid enantiomers

Gaudichaudianic acid, a prenylated chromene isolated from Piper gaudichaudianum, has been described as a potent trypanocidal compound against the Y-strain of Trypanosoma cruzi. We herein describe its isolation as a racemic mixture followed by enantiomeric resolution using chiral HPLC and determination of the absolute configuration of the enantiomers as (+)-S and (-)-R by means of a combination of electronic and vibrational circular dichroism using density functional theory calculations. Investigation of the EtOAc extract of the roots, stems, and leaves from both adult specimens and seedlings of P. gaudichaudianum revealed that gaudichaudianic acid is biosynthesized as a racemic mixture from the seedling stage onward. Moreover, gaudichaudianic acid was found exclusively in the roots of seedlings, while it is present in all organs of the adult plant. Trypanocidal assays indicated that the (+)-enantiomer was more active than its antipode. Interestingly, mixtures of enantiomers showed a synergistic effect, with the racemic mixture being the most active.

Chemistry and Biological Activity of Essential Oils from Piper Claussenianum (Piperaceae)

Analyses of essential oils obtained from fresh and dried leaves and inflorescences of Piper clausenianum were performed using GC-FID, GC-MS and NMR techniques. Forty compounds were detected for these four oils with the total of identified constituents ranging from 88.7% for the dried inflorescences to 97.7% for the dried leaves. Sesquiterpenes were the main constituents in the volatile fraction from leaves with a high percentage of ( E)-nerolidol (up to 83%). However, monoterpenes were identified in greater amount in the inflorescences, with linalool percentages from 50% up. The essential oils from fresh leaves and inflorescences were submitted to anti-parasitic activity against a strain of Leishmania amazonensis. Both samples showed biological activity, but the essential oil from P. claussenianum fresh leaves, which was rich in ( E)-nerolidol, showed effective growth inhibition of L. amazonensis due to the high percentage of this metabolite in the mixture.

C-glycosyl flavones from Peperomia blanda

The methanol extract from aerial parts of the Peperomia blanda (Piperaceae) yielded two C-glycosyl-flavones. Their structures were elucidated on the basis of extensive spectroscopic analysis, including 1D and 2D NMR, chemical transformation and comparison with the related known compounds. The structure of the new flavonoids were established as 4'-methoxy-vitexin 7-O-beta-D-xylopyranoside (1) (7-O-beta-D-xylopyranosyl-8-C-beta-D-glucopyranosyl-4'-methoxy-apigenin) and vicenin-2 (2). The antioxidant activity of both compounds was investigated using the DPPH assay. Both compounds showed only modest activity, with IC50 values of 357.2 microM for 1, and 90.5 microM for 2.

Petiolins A-C, phloroglucinol derivatives from Hypericum pseudopetiolatum var. kiusianum

Two new phloroglucinol derivatives possessing chromane skeleton, petiolins A (1) and B (2), and a new phloroglucinol derivative containing a dihydrofuran ring, petiolin C (3), were isolated from aerial parts of Hypericum pseudopetiolatum var. kiusianum. The gross structures of 1-3 were elucidated by spectroscopic data, and the relative stereochemistry of 3 was elucidated by NOESY data. Petiolins A-C (1-3) showed modest cytotoxicity, while petiolin C (3) exhibited antifungal activity.

Trypanocidal tetrahydrofuran lignans from Peperomia blanda

Five tetrahydrofuran lignans and two known flavones were isolated from the aerial parts of Peperomia blanda. The structures of the isolated lignans were elucidated by interpretation of their spectroscopic data, including by gHMQC and gHMBC. The relative and absolute configurations of the isolates were determined from NOESY interactions and optical properties, respectively. Four of the lignans were diastereomeric whilst one was of mixed biosynthetic origin. All but one of the lignans exhibited high in vitro trypanocidal activity when assayed against epimastigotes of Trypanosoma cruzi strain Y.