Parthenolide (PTN) is a secondary metabolite of the plant Tanacetum parthenium (L.) Schulz Bip. and is considered the chemical marker of this species. This sesquiterpene lactone (germacrene skeleton) has been described as responsible for the biological activity of the leaf extract. In addition, several studies in the literature have demonstrated its antiparasitic and antineoplastic activity. However, there is a need for knowledge of other safety parameters, such as pharmacokinetic, pharmacodynamic and toxicity evaluations. Therefore, in this investigation, the in vitro metabolism of parthenolide was performed with rat liver microsomes and biomimetic metabolism (such as cytochrome P-450 system) using organometallic catalysts. The biomimetic procedure was validated since the major compound of biomimetic oxidative reaction with meta-chloroperbenzoic acid catalyzed by metalloporphyrin 5,10,15,20-tetrakis(pentafluorophenyl)-porphyrin iron(III) chloride was also observed with rat liver microsomes. Previous chemoenzymatic synthesis studies of PTN afforded the same epoxide formation, this major oxidative compound was isolated and fully characterized as (1 R,10R)-epoxyparthenolide based on experimental and theoretical calculations of infrared (IR) and vibrational circular dichroism (VCD) data at the B3PW91/6-311G. Furthermore, for the first time, this metabolite was evaluated for trypanocidal and leishmanicidal activity. The mean inhibitory concentration (IC50) values were lower for PTN than its metabolite and showed significant cytotoxic effects for both parasites. This finding holds promise for addressing neglected diseases. (PTN L. L (L. Bip species germacrene skeleton extract addition However parameters pharmacokinetic evaluations Therefore investigation P450 P 450 P-45 system catalysts metachloroperbenzoic meta chloroperbenzoic 5,10,15,20tetrakispentafluorophenylporphyrin 5101520tetrakispentafluorophenylporphyrin tetrakispentafluorophenylporphyrin 5,10,15,20 tetrakis pentafluorophenyl porphyrin 5 10 15 20 ironIII iron III iron(III formation 1 ( R,10Repoxyparthenolide R10Repoxyparthenolide RRepoxyparthenolide R,10R epoxyparthenolide R 10R IR (IR VCD (VCD B3PW91/6311G. B3PW916311G BPWG B3PW91/6 311G. B3PW91 6 311G B PW G B3PW91/6-311G Furthermore time IC50 IC (IC50 parasites diseases (L P45 45 P-4 20tetrakispentafluorophenylporphyrin 5101520 5,10,15,2 2 10Repoxyparthenolide Repoxyparthenolide R10R RR 6311G B3PW91/6311G B3PW916 BPW B3PW91/ B3PW9 IC5 (IC5 P4 4 P- 510152 5,10,15, B3PW (IC 51015 5,10,15 5101 5,10,1 510 5,10, 51 5,10 5,1 5,

The assignment of absolute configuration (AC) is a crucial step in the structural characterization of natural products, especially for those subjected to biological assays. Methods such as X-ray crystallography, stereocontrolled organic synthesis, nuclear magnetic resonance (NMR), and chiroptical spectroscopies are commonly used to determine the AC of chiral natural compounds. Even with these well-established techniques, however, unambiguous stereochemical assignments of natural products remain a challenge, resulting in an increasing number of structural misassignments being reported every year. Herein, we will present the main techniques that have been used in AC reassignments of natural products over the last 10 years, along with some selected examples. Special attention will be paid to the strengths and weaknesses of each approach. With this, we expect to provide the readers with critical information to help them to choose the appropriate methods for correct AC determinations.

The phytochemical study of Hippeastrum goianum led to the identification of 13 compounds by means of gas chromatography-mass spectrometry (GC-MS) and nuclear magnetic resonance (NMR). Compounds 7-demethoxy-9-O-methylhostasine (1) and 7-deoxi-trans-dihydronarciclasine (2) had their absolute configurations determined by vibrational circular dichroism (VCD). This is the first time that compound 1 is described in the Amaryllidaceae family. The cytotoxicity of all isolated compounds was tested against colorectal carcinoma (HCT 116), breast carcinoma (MCF-7), and non-tumor human retinal pigment epithelium (RPE) cell lines. The half-maximum inhibitory concentration (IC50) of compound 2 against each cell line was equivalent to the positive control (doxorubicin), indicating a considerable cytotoxic activity.

The antibiotic streptazolin (1), its E-isomer (2), along with the stereoisomers strepchazolin A (3) and strepchazolin B (4) and the inorganic compound cyclooctasulfur (5) were produced in solid culture by Streptomyces chartreusis ICBG377, which was isolated from the fungal garden of the leaf-cutter ant Acromyrmex subterraneus brunneus. This is the first time compound 2 is reported as a natural product. Compound 5, which showed antagonist activity against the specialized pathogenic fungus Escovopsis sp., was also produced by Streptomyces chartreusis ICBG323, isolated from the exoskeleton of winged male of Mycocepurus goeldii. The absolute configurations of 3 and 4 were confirmed by the combination of vibrational circular dichroism (VCD) spectroscopy and density functional theory (DFT) calculations. These results clearly demostrate the power of VCD to tell apart epimeric natural products. Compounds 1, 3 and 4 were produced by geographically distant but phylogenetically close strains, S. chartreusis ICBG 377 isolated in Brazil, and S. chartreusis NA02069, a marine sediment strain isolated in China.

Piper gaudichaudianum Kunth (Piperaceae) accumulates gaudichaudianic acid, a prenylated benzopyran, as its major component. Interestingly, this trypanocidal compound occurs as a racemic mixture. Herein, transcriptomic investigations of Piper gaudichaudianum using the RNA-seq approach are reported, and from the analysis of the transcripts expressed it was possible to propose a complete biosynthetic pathway for the production of gaudichaudianic acid, including the steps that originate its precursor, p-hydroxybenzoic acid. Peperomia obtusifolia (L.) A. Dietr. (Piperaceae) also accumulates racemic benzopyrans, however, its chromanes originate from the polyketide pathway, while the chromenes from Piper derives from the shikimate pathway. Recent transcriptomic and proteomic studies of the former species did not identify polyketide synthases involved in the production of the benzopyran moiety, but revealed the expression of tocopherol cyclase, which may be responsible for the cyclization of the 3,4-dihydro-2H-pyran ring. The analysis of the enzymes involved in the secondary metabolism of Piper gaudichaudianum and the comparison with the data previously obtained from Peperomia obtusifolia can provide valuable information on how these compounds are biosynthesized.