Alstolarines A and B, two unusual monoterpenoid indole alkaloids with an acetal moiety from Alstonia scholaris

• Published in: ORGANIC CHEMISTRY FRONTIERS Vol. 7; no. 21; pp. 3468 - 3473
• Main Authors: Zhang, Jian, Song, Min, Ao, Yun-Lin, Li, Yong, Zou, Xue-Yi, Xu, Jie, Wang, Ying, Zhang, Dong-Mei, Zhang, Xiao-Qi, Ye, Wen-Cai
• Format: Journal Article
• Language: English
• Published: CAMBRIDGE Royal Soc Chemistry 07.11.2020; Royal Society of Chemistry
• Subjects: Acetylcholinesterase; Alkaloids; Alstonia scholaris; Chemistry; Chemistry, Organic; Circular dichroism; Computer applications; Crystallography; Dichroism; Indoles; NMR; Nuclear magnetic resonance; Organic chemistry; Physical Sciences; Science & Technology; Single crystals; X-ray diffraction; ACIDS
• ISSN: 2052-4129; 2052-4110; 2052-4110
• DOI: 10.1039/d0qo00751j

Two novel monoterpenoid indole alkaloids, alstolarines A and B (1-2), were isolated from the leaves and twigs of Alstonia scholaris. Compound 1 is the first vobasinyl-type alkaloid with a 6/5/8/5/6/5 hexacyclic architecture featuring an unprecedented 21-oxa-4-azaspiro[4,4]nonane unit. Compound 2 is the first 21-nor-vobasinyl-type alkaloid with a unique 3-oxa-4-azatricyclo[5.1.1.1(3,20)]undecane ring system. Their structures including absolute configurations were established by a combination of spectroscopic data analyses, electronic circular dichroism (ECD) calculations, and single crystal X-ray diffraction analysis. The plausible biogenetic pathways of 1 and 2 were also proposed. Compounds 1 and 2 exhibited promising vasorelaxant activities with EC50 values of 4.6 and 6.7 mu M, and compound 2 showed moderate acetylcholinesterase (AChE) inhibitory activity with an IC50 value of 19.3 mu M.