Structurally diverse monoterpene indole alkaloids with vasorelaxant activities from the branches of Alstonia scholaris

N-acetyldopamine oligomers from Periplaneta americana with anti-inflammatory and vasorelaxant effects and their spatial distribution visualized by mass spectrometry imaging

ETHNOPHARMACOLOGICAL RELEVANCE

Periplaneta americana is a medicinal insect that has been applied to promote blood circulation and remove blood stasis based on traditional Chinese medicine (TCM) for a long time. Its modern preparation, Xinmailong injection, was adopted for the treatment of congestive heart failure (CHF). The bioactive constituents of P. americana and their correlation with its traditional uses need further investigation.

AIM OF THE STUDY

This study aimed to elucidate the N-acetyldopamine (NADA) oligomers from P. american, determine their spatial distribution, and investigate their anti-inflammatory and vasorelaxant effects to provide scientific evidence supporting the clinical use of this medicinal insect.

MATERIAL AND METHODS

NADA oligomers were isolated from the CH2Cl2: CH3OH (2:1) extract of P. americana, through sequential chromatographic methods including silica gel, Sephadex LH-20, preparative HPLC, and chiral-phase separation. Their structures were determined by HRESIMS, 1D and 2D NMR spectroscopic analysis, chiral resolution, and calculated electronic circular dichroism analysis. With the aid of atmospheric pressure scanning matrix-assisted laser desorption/ionization mass spectrometry imaging (AP-SMALDI MSI), the isolated compounds in a spatial profile within P. americana were identified. NO production was measured to assess anti-inflammatory activity. Vasorelaxant activity assessments were performed on the norepinephrine-precontracted 3rd-order mesenteric arteries.

RESULTS

Seven new NADA trimers, peridopamines A-G (1-7), two new NADA dimers, peridopamines H and I (8 and 9), and six known NADA derivatives (10-15), were obtained from P. americana. The trimers and dimers were detected and showed similar pattern of distribution with accumulation in peripheral and rigid parts of P. americana, based on quasimolecular ion AP-SMALDI MS images of sections from the whole body and dissected areas of the insect. Furthermore, the anti-inflammatory and vasorelaxant effects of isolated compounds were investigated. Compounds 8 and 9 presented significant and moderate anti-inflammatory potentials, respectively. Compounds 8, 10, 12 and 15 possess significant vasorelaxant potentials at concentrations correlated with EC50 values of 6.7-23.7 μM.

CONCLUSION

Fifteen NADA oligomers were isolated from P. americana. The distribution of these compounds was visualized by AP-SMALDI imaging experiments and NADA oligomers were mainly observed in peripheral parts. Bioassays showed that the tested compounds had anti-inflammatory and vasorelaxant activities, which indicated that NADA oligomers are active ingredients of this insect-based TCM and have potential for the treatment of cardiovascular disease.

Polycyclic pyrroloindoline-containing natural products with a unique 3-heptyl-2a,4a-diazapentaleno[1,6-ab]indene core isolated from Alstonia scholaris

Alscholarine C (1), featuring an unprecedented pyrroloindoline-containing natural product (PiNP) with a 6/5/5/5 tetracyclic carbon skeleton, and four known PiNPs (2-5), namely demethylalstoscholarinine E (2), Nb-demethylechitamine (3), winphylline A (4), and echitamine (5), were isolated from Alstonia scholaris. Compound 1 was characterized by a hexahydropyrrolo[2,3-b] indole (HPI) core fused to a unique 4-heptylimidazolidine motif, forming an unparalleled 3-heptyl-2a,4a-diazapentaleno[1,6-ab]indene ring system. Their structures were established by spectroscopic analysis, quantum-chemical calculated 13C NMR data with DP4+ probability analyses, and ECD calculations and comparison. A plausible biosynthetic pathway of 1 was proposed. Compound 1 exhibited potential anti-inflammatory activity against LPS-stimulated NO production in RAW264.7 cells.

Monoterpene indole alkaloids from the roots of Alstonia rupestris and their anti-inflammatory activity

Four new monoterpene indole alkaloids (1-4) together with twelve known alkaloids (5-16) were isolated from the roots of Alstonia rupestris. Compound 1 was the first example of C2-symmetric heteroyohimbine-type indole alkaloid homodimer obtained from natural plant resource. Their structures were elucidated on the basis of spectroscopic data. The absolute configuration of 1 was determined by comparison of its calculated and experimental electronic circular dichroism (ECD) spectra. All compounds were evaluated for their anti-inflammatory activities by measuring their NO inhibitory effects in LPS-stimulated RAW 264.7 cells. Compound 2 showed strong NO inhibition with IC50 value of 4.2 ± 1.3 μM. Moreover, compound 2 could decrease the expressions of cyclooxygenase-2 (COX-2) and transforming growth factor beta-1 (TGF-β1).

Alscholarines A and B, two rearranged monoterpene indole alkaloids from Alstonia scholaris

Alscholarines A and B (1 and 2), two unprecedented rearranged monoterpene indole alkaloids, were isolated from Alstonia scholaris. Alscholarine A (1) features an imidazole ring fused with a rearranged vallesamine-type alkaloid possessing an unparalleled 6/5/6/6 tetracyclic skeleton through an unprecedented C7-C-19 connectivity. Alscholarine B (2), incorporating an unusual 7-oxa-1-azabicyclo[3.2.1]octane moiety, represents a unique rearranged vallesamine-type alkaloid with a 6/5/6/6/5 ring system via an unprecedented C-6-C-20 connectivity. Their structures were established by spectroscopic analysis, X-ray crystallography, and quantum-chemical calculations. Their plausible biosynthetic pathways were proposed. The vasorelaxant and anti-inflammatory activities of them were also evaluated. Compounds 1-3 showed moderate vasorelaxant activities.