Isolation and Elucidation of 15-Acetylguanacone from Soursop (Annona muricata Linn) Fruit and Molecular Docking Experiments

Abstract

Annona muricata (Soursop) has attracted attention due to its content of annonaceous acetogenins, a large family of naturally occurring polyketides isolated from various species of the genus Annonaceae. The ethyl acetate fraction of Annona muricata was subjected to standard isolation protocol-gradient and isocratic silica gel column chromatography- to obtain three waxy and whitish amorphous compounds, 002/A1, 002/A2 and 002/C. The structure of compound 200/A2 was elucidated using ¹H-NMR spectroscopy, infrared spectroscopy and electron impact (EI+) mass spectroscopy. The molecular weight of 200/A2 was determined as 662 by EI-MS ([M+H]+ : m/z = 662.1) leading to the molecular formula C₃₉H₆₆O₈ as obtained using high resolution MS. The existence of an α, β-unsaturated γ-lactone moiety, non-hydroxylated at the C-4 position, was suggested by an IR carbonyl absorption at 1735.9 cm^-1 and 1662.7 cm^-1; the IR also gave signal for hydroxyl group at 3339.0 cm^-1. The presence of a characteristic vinyl proton δ 7.24 (H-35, d), which is characteristic for α, β- unsaturated γ-lactone was confirmed by the ¹H-NMR spectrum. The compound was thus elucidated to be 15-acetyl guanacone, an acetogenin. This acetogenin has not been reported in Annona muricata previously. The compound was subsequently subjected to molecular docking experiments which revealed that it targets and binds to vascular endothelial growth factor 2, VEGF2 (-8.5kcal/mole) and α1 β2 integrin (-6.8kcal/mole), This thus suggests that 15-acetyl guanacone prevents metastasis and invasion by cancer cells, and ultimately initiates apoptosis.

Key words: VEGF2; Integrin; Cancer; Acetogenins; Apoptosis; Soursop.