Seven new germacranolides (1–3, 5–8), among them a heterodimer (7), and known germacranolide (4), eudesmane (9) and isodaucane (10) sesquiterpenes were isolated from the aerial parts of Neurolaena lobata. Their structures were determined by using a combination of different spectroscopic methods, including HR-ESIMS and 1D and 2D NMR techniques supported by DFT-NMR calculations. The enantiomeric purity of the new compounds was investigated by chiral HPLC analysis, while their absolute configurations were determined by TDDFT-ECD and OR calculations. Due to the conformationally flexible macrocycles and difficulties in assigning the relative configuration, 13C and 1H NMR chemical shift and ECD and OR calculations were performed on several stereoisomers of two derivatives. The isolated compounds (1–10) were shown to have noteworthy antiproliferative activities against three human cervical tumor cell line with different HPV status (HeLa, SiHa and C33A). Additionally, lobatolide C (6) exhibited substantial antiproliferative properties, antimigratory effect, and it induced cell cycle disturbance in SiHa cells.
Epimeric
series of aryl-substituted glucopyranosylidene-spiro-imidazolinones,
an unprecedented new ring system, were synthesized from the corresponding
Schiff bases of O-perbenzoylated (gluculopyranosylamine)onamides
by intramolecular ring closure of the aldimine moieties with the carboxamide
group elicited by N-bromosuccinimide in pyridine.
Test compounds were obtained by Zemplén O-debenzoylation.
Stereochemistry and ring tautomers of the new compounds were investigated
by NMR, time-dependent density functional theory (TDDFT)-electronic
circular dichroism, and DFT-NMR methods. Kinetic studies with rabbit
muscle and human liver glycogen phosphorylases showed that the (R)-imidazolinones were 14–216 times more potent than
the (S) epimers. The 2-naphthyl-substituted (R)-imidazolinone was the best inhibitor of the human enzyme
(K
i 1.7 μM) and also acted on HepG2
cells (IC50 177 μM). X-ray crystallography revealed
that only the (R) epimers bound in the crystal. Their
inhibitory efficacy is based on the hydrogen-bonding interactions
of the carbonyl oxygen and the NH of the imidazolinone ring.
The first members of a new alkaloid class, chaetolines A (1) and B (2), which feature a pyrano[3,2f ]isoquinoline core structure, were obtained from a crude extract of the fungal endophyte Chaetomium sp. after cultivation in the presence of autoclaved Pseudomonas aeruginosa. The structures of the new compounds, including the absolute configuration of the major stereoisomer, were determined through detailed analysis of HRESIMS, 1D/2D NMR, and calculation of ECD data. The possible biosynthetic origin of the unprecedented scaffold of 1 and 2 is proposed. The current study provides further evidence for mixed fermentation as a powerful tool to induce the accumulation of cryptic fungal natural products even in the absence of viable bacterial cells.
Two new carotenoids, sapotexanthin 5,6-epoxide and sapotexanthin 5,8-epoxide, have been isolated from the ripe fruits of red mamey (Pouteria sapota). Sapotexanthin 5,6-epoxide was also prepared by partial synthesis via epoxidation of sapotexanthin, and the (5R,6S) and (5S,6R) stereoisomers were identified by high-performance liquid chromatography-electronic circular dichroism (HPLC-ECD) analysis. Spectroscopic data of the natural and semisynthetic derivatives obtained by acid-catalyzed rearrangement of cryptocapsin 5,8-epoxide stereoisomers were compared for structural elucidation.
K E Y W O R D Scarotenoid, deoxy kappa end group, HPLC-ECD, semisynthesis, structure elucidation
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