STRUCTURAL MODIFICATIONS OF POTENTIAL RECEPTOR BINDING GROUPS OF STEVIOL

1. Introduction References STRUCTURAL MODIFICATIONS OF POTENTIAL RECEPTOR BINDING GROUPS OF STEVIOL Sandra Hojniak*, Nico Moons Geïntegreerd Projectpracticum, 3e Bachelor Chemie, K.U.Leuven, Departement Chemie, Celestijnenlaan 200F, B-3001 Leuven (Heverlee). E-mail: sandra.hojniak@student.kuleuven.be Following the path 2, we first eliminated the difficulties in performing the column separation (presence of –COOH group) by changing the polarity by esterification. We activated than the vinylic group for nucleophilic substitution by epoxidation. Stevioside is a natural sweetener 300 times sweeter than sucrose, obtained from the South American plant Stevia rebaudiana. It is attracting substantial scientific interest owning to its biological activity in vivo. Stevioside has the ability to decrease the blood pressure and blood glucose level in hypertensive patients and patients with type-2 diabetes respectively, with no adverse effects. It does not moreover influence healthy patients in general [1]. Exact mechanisms of those phenomena have not been discovered yet but they are, as suggested, based on the ligand-receptor interaction[2](most probably receptors controlling the ionic channels). Therefore there is an increasing demand on achieving diversely functionalised derivatives of the title molecule in order to determine which of the structural units are responsible for the activity. Table 1: Yields of the performed reactions Methodology • *product not purified yet from benzylamine, due to the time constraints • The major impurity in the epoxide -yield >100% (Table 1) was the ester (TLC). The next steps (c,d) were performed in a consecutive manner, without further purification of the epoxide, since ester does not react with the amine . • After evaporating the reaction solvent and applying column solvent to the product (6), we observed a fast and substantial appearance of white crystals. MS check showed a pure 3-methylpiperidine spectrum, which simplified the column purification. In order to obtain structural derivatives of steviol we concentrated on the 1st of the paths presented : Scheme 1: Synthetic pathways 1 and 2 1 further derivatives a steviol (SV) (2) 1H NMR of (6) 2 b isosteviol (ISV) (3) stevioside (1) • (a) NaIO4, in H2O, KOH, AcOHglacial • (b) HBr 48% , 12h, rt, column – 3/7 heptane /EtOAc • Initially, (1) was obtained from the dried leaves of Steviaby 2 water extractions and purification on Amberlite IRA-400 (CI)-column. Small yield <1% (Table 1) could have been caused by a few factors: insufficient eluting, poor condition of the Amberlite or not performed 3rd extraction. • Syntheses of steviol and isosteviol were based on the laboratory stevioside supplies. Discussion and Conclusions Scheme 2: Synthetic pathway 1 • Performed modifications on steviol and especially stereospecific reaction with amines open large possibilities towards obtaining a big variety of valuable compounds for determining the stevioside effect on humans. • Amines are relatively cheap and these reactions do not require special conditions. Structures varying only with one substituent on C17 with different size and functional groups, may allow to determine interactions at one certain region of the receptor binding site. • The use of microwave irradiation for the amines preparation could shorten the reaction time. a b (5) (4) (2) c d (6) (7) (a) Cs2CO3(2 eq.), MeOH, rt 0.5 h ,MeI (5 eq.), DMSO, rt, 1h, lyophilized(b)mCPBA (3 eq.),DCM, column 6/4 heptane/EtOAc,(c) 4-methylpiperidine (9 eq.), MeOH, reflux 48 h, column 3/7 heptane/EtOAc +1% AcOH, product eluted with 9/2 CHCl3/MeOH +1% Et3N, (d)benzylamine (9 eq.), MeOH, reflux 60 h, column-DCM +1% MeOH+ 1% Et3N [1]Benford, D.J.; DiNovi, M., Schlatter, J. (2006). “Safety Evaluation of Certain Food Additives: Steviol Glycosides, WHO Food Additives Series 54: 140 [2] Prof. J.M.C. Geuns, Situation of stevioside in the world. Report of the 63rd Jecfa Meeting, 8-17 June 2004.