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Reddy, Kaylan [1], Stafford, Gary Ivan [2], Makunga, Nokwanda [3].

Sceletium Secrets - Exploring the phytochemical and metabolomic diversity in the Sceletium genus.

The Sceletium genus has been of medicinal importance in southern Africa for millennia, used by the indigenous KhoiSan people [1]. Recently, a species from the genus has gained pharmaceutical importance as an anxiolytic and anti-depressant, and some of the phytochemicals have been studied. However, there is a general lack of information with regards to the other species in the genus. The major chemical class thought to be responsible for the anxiolytic activity has been the mesembrine alkaloids [2,3] but in silico results presented here tentatively show potential of other chemical classes with neuro-pharmacological potential. The first aim of the study was to investigate the chemical diversity present in the Sceletium genus through in silico molecular docking, using the virtual screening protocol of Schrodinger’s Glide. Phytochemicals known to occur in Sceletium plants were subjected to computational target fishing using reverse in silico screening on the 5-HT serotonin transporter (5I75), the GABA-A receptor (6D6T), the MAO-B monoaminoxidase-B (2XFU) the PDE4B phosphodiesterase-4 (3D3P) and AChE acetylcholinesterase (1QTI) target sites to provide deeper insights into their neurobiological binding potential. The second aim of the study was to use metabolomic based tools to identify key differences between species and populatioins. We have identified interesting chemical diversity across the genus. Great chemical diversity was found at an inter-species level.
Dihydrojoubertiamine (-6.497 ∆kcal/mol), Sceletenone (-6.308 ∆kcal/mol), 3’-methoxy-4’-O-methyljoubertiaminol (-6.280 ∆kcal/mol) and 4'-O-demethylmesembranol (-6.096 ∆kcal/mol) showed the highest binding affinity in static simulations against the GABA-A receptor. The compounds satisfied Lipinski’s rule of five and showed good predictive oral absorptivity. The ADMET properties of the compounds were also determined as an assesment of drugability. Plant samples were collected from the wild (Karoo, South Africa) and analysed through LC-MS, using MSE fragmentation as a putative tool for chemical identities. These compounds occurred at variable levels in Sceletium ecotypes. In silico analysis and metabolomics and proved as useful tools in analysing the phytochemical and pharmacological diversity within the Sceletium genus and informing future in vitro and in vivo study design.
1. Gericke, N. and Viljoen, A. M. (2008) ‘Sceletium-A review update’, Journal of Ethnopharmacology, 119(3), pp. 653–663.
2. Harvey, A. L. et al. (2011) ‘Pharmacological actions of the South African medicinal and functional food plant Sceletium tortuosum and its principal alkaloids’, Journal of ethnopharmacology. Elsevier, 137(3), pp. 1124–1129.
3. Krstenansky, J. L. (2017) ‘Mesembrine alkaloids: Review of their occurrence, chemistry, and pharmacology’, Journal of Ethnopharmacology. Elsevier, 195(December 2016), pp. 10–19.

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1 - Stellenbosch University, Faculty of Science Stellenbosch University Private Bag X1 Matieland 7602, South Africa, Stellenbosch, Western Cape, 7602, South Africa
2 - University of Pretoria, Plant and Soil Sciences, Room 3-15, Level 3, Plant Sciences Complex University of Pretoria, Private Bag X20 , Hatfield 0028, South Africa, Pretoria East, Gauteng, 0028, South Africa
3 - Room 1087 Department Of Botany And Zoology, Merriman Avenue Matieland, Stellenbosch, WC, 7602, South Africa

in silico

Presentation Type: Poster
Session: P2, Ethnobotany Posters
Location: Virtual/Virtual
Date: Tuesday, July 20th, 2021
Time: 5:00 PM(EDT)
Number: P2ET004
Abstract ID:703
Candidate for Awards:Economic Botany Section best poster

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