Alkaloids from Alstonia scholaris and Ficus schwarzii

Krishnan, Premanand (2022) Alkaloids from Alstonia scholaris and Ficus schwarzii. PhD thesis, University of Nottingham.

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Alkaloids, which are the most studied secondary metabolites, are structurally diverse and well known for their biological activity. The aim of the present study is to perform phytochemical investigations on the alkaloidal composition of two selected plant species, namely, Ficus schwarzii (Moraceae) and Alstonia scholaris (Apocynaceae). (specimen from the West Coast of Peninsular Malaysia). The previously unexplored phytochemistry of F. schwarzii and the phytochemical variation of A. scholaris due to locality have motivated research into the two species collected from Peninsular Malaysia.

Phytochemical investigation of the leaves of F. schwarzii yielded nine novel alkaloids, namely, schwarzinicines A−G (1−7), and schwarzificusines A and B (8 and 9). The schwarzinicine alkaloids represent the first examples of 1,4 diarylbutanoid−phenethylamine conjugates, while schwarzificusines A and B (8 and 9) represent a pair of new diastereomeric 1-phenyl-3-aminotetralins that are structurally related to the schwarzinicines alkaloids. The structures of alkaloids 1–9 were elucidated by detailed analysis of their HRMS and NMR data. Plausible biogenetic pathways that furnish the skeletons of the schwarzinicine and schwarzifiscusine alkaloids were proposed.

Phytochemical investigation of the leaves, bark and flowers of A. scholaris cultivated on the West Coast of Peninsular Malaysia provided a total of 17 alkaloids, of which five are new, namely, alstoscholactine (10), alstolaxepine (11), N-formylyunnanensine (12), scholaphylline (13), and alstobrogaline (19). Alstoscholactine (10), alstolaxepine (11), and alstobrogaline (19) were established to contain novel ring systems. Alstoscholactine (10) represents a rearranged stemmadenine alkaloid with an unprecedented C-6-C-19 connectivity, while alstolaxepine (11) represents a 6,7-seco-angustilobine B-type alkaloid incorporating a rare γ-lactone-bridged oxepane ring system. On the other hand, alstobrogaline (19) is an unusual monoterpenoid indole alkaloid incorporating a third N atom, and possessing an aldimine as well as a nitrone function. N-Formylyunnanensine (12) is the N-formyl derivative of the known alkaloid yunnanensine, and it was isolated as a pair of unseparable E/Z-formamide rotamers. Scholaphylline (13) represents the first member of the secostemmadenine-secovallesamine-type bisindole alkaloid. The 12 known alkaloids obtained from Alstonia scholaris are 19,20-E-vallesamine (14), 19,20-Z-vallesamine (15), 19,20-E-vallesamine N-oxide (16), 6,7-secoangustilobine B (17), and 6,7-seco-19,20-epoxyangustilobine B (18), tetrahydroalstonine (20), picrinine (21), 16R-19,20-Z-isositsirikine (22), 16R-19,20-E-isositsirikine (23), scholaricine (24), N-demethylalstogustine N-oxide (25), and E/Z-vallesiachotamine (26).

Item Type: Thesis (University of Nottingham only) (PhD)
Supervisors: Lim, Kuan Hon
Low, Yun Yee
Keywords: alkaloids, phytochemical investigation, Ficus schwarzii (Moraceae), Alstonia scholaris (Apocynaceae)
Subjects: R Medicine > RC Internal medicine
Faculties/Schools: University of Nottingham, Malaysia > Faculty of Science and Engineering — Science > School of Pharmacy
Item ID: 69459
Date Deposited: 24 Jul 2022 04:40
Last Modified: 16 Sep 2022 12:30

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