Michellamines A6 and A7, and further mono- and dimeric naphthylisoquinoline alkaloids from a Congolese Ancistrocladus liana and their antiausterity activities against pancreatic cancer cells.

Blaise Kimbadi Lombe,Virima Mudogo,Suresh Awale,Gerhard Bringmann,Doris Feineis,Reto Brun

doi:10.1039/c8ra00363g

Abstract

Michellamines A6 (1) and A7 (2) are the first dimers of 5,8′-coupled naphthylisoquinoline alkaloids with cis-configured stereocenters in both tetrahydroisoquinoline subunits. They were isolated from the leaves of a recently discovered, yet unidentified Congolese Ancistrocladus liana that shares some morphological characteristics with Ancistrocladus likoko. Two further new dimeric analogs, michellamines B4 (3) and B5 (4), were obtained, along with two previously likewise unknown monomers, ancistrobonsolines A1 (5) and A2 (6), which, besides one single known other example, are the only naphthyldihydroisoquinolines with an M-configured biaryl axis and R-configuration at C-3. Moreover, five compounds earlier reported from other Ancistrocladus species were identified, ancistroealaine C (7), korupensamines A (8a) and B (8b), and michellamines A2 (9) and E (10). Their complete structural elucidation succeeded due to the fruitful interplay of spectroscopic, chemical, and chiroptical methods. Chemotaxonomically, the stereostructures of the metabolites clearly delineate this Congolese Ancistrocladus liana from all known related species, showing that it might be a new taxon. Ancistrobonsolines A1 (5) and A2 (6) exhibited strong preferential cytotoxicities against human PANC-1 pancreatic cancer cells under nutrient-deprived conditions, without displaying toxicity in normal, nutrient-rich medium. Against cervical HeLa cancer cells, the dimeric alkaloids michellamines A6 (1) and E (10) displayed the highest cytotoxic activities, comparable to that of the standard agent, 5-fluorouracil. Furthermore, ancistrobonsolines A1 (5) and A2 (6) showed weak-to-moderate antiprotozoal activities.

Highlights

Plants belonging to the genus Ancistrocladus Wall. (Ancistrocladaceae) continue to receive much attention, mainly because they produce a class of structurally, biosynthetically, and pharmacologically unusual compounds, the naphthylisoquinoline alkaloids.[1]
The number of Congolese Ancistrocladus species may, be much higher, as there have not yet been thorough and speci c botanical campaigns covering the entire Congolese forest, which is so vast and so rich in biodiversity. This assumption is supported by recent phylogenetic investigations on Ancistrocladus samples collected at different sites in Democratic Republic of the Congo (DRC),[6] which hinted at the presence of a potentially new taxon from the region near the village Bonsolerive, close to the town Mbandaka, in the northwestern part of DRC
Extraction of the air-dried leaves with a mixture of methanol and dichloromethane (1 : 1), followed by concentration under reduced pressure, provided a crude residue, which was submitted to a cation-exchange column to remove undesired, non-basic metabolites

Summary

Introduction

Plants belonging to the genus Ancistrocladus Wall. (Ancistrocladaceae) continue to receive much attention, mainly because they produce a class of structurally, biosynthetically, and pharmacologically unusual compounds, the naphthylisoquinoline alkaloids.[1]. These correlations, together with the known R-con guration at C-3 (see above), evidenced the southeastern biaryl axis to be M-con gured, showing the corresponding moiety to have the same structure as the likewise isolated korupensamine B (8b) (Fig. 4b).

Results

Conclusion