Synthesis, Characterization and Alpha Glucosidase Inhibition Activity of New Phthalimide Derivatives

100 Synthesis, Characterization and Alpha Glucosidase Inhibition Activity of New Phthalimide Derivatives Hassan A. M. Jawed, Mohammed H. Mohammed and Sajida H. Ismeal * Department of Pharmaceutics Chemistry, College of Pharmacy , University of Al-Mustansiriya Baghdad ,Iraq. Department of Pharmaceutics Chemistry, College of Pharmacy, University of Baghdad, Baghdad ,Iraq. *** Department of Pharmacology and Toxicology, College of Pharmacy, University of Baghdad, Baghdad, Iraq. Abstract Three of intermediate imide compounds were synthesized through reacting of phthalic anhydride with glycine(compound2a), and tetrachlorophthalic anhydride with glycine, (S)-2-[(tertButoxycarbonyl)amino]-3-aminopropionic acid(compounds2b,c) respectively in dry toluene with azeotropic removal of water using Deanstark apparatus then carboxyl functional group activated by refluxing with thionyl chloride, the resulted acid chloride(compounds 3a-c) were reacted with different amine (5-flourouracil, 4-chloroaniline, 4-bromoaniline, 2-amino thiazole, and pyrrolidine)(compounds 4a-e) , the compounds (5a-j)consider as end productswhile the compounds (5k-o) required further reaction to deprotect aliphatic amine this was achieved by treating the compounds with trifloruro acetic acid (TFA) to remove tert-Butoxycarbonyl group (compounds 6a-e). The alpha glucosidase inhibitory activity of some synthesized compounds(5a, 5f, 6a)was evalutedagainst alpha-glucosidase enzyme extracted from Saccharomyces bacteria, p-αnitrophenol glucopyranoside (pNPG) was used as substrate and thestandard was acarbose. All these test compounds showsexcellent inhibitory activity according to IC50 values which is ranging from (4.61-7.32 M).


Introduction
Diabetes mellitus (DM) is a chronic metabolic disorder with heterogeneous etiologies )genetic and environmental factors(, it is characterized by disturbance in the metabolisms of carbohydrate, fat and protein resulting from defects in insulin secretion, insulin action or both (1)(2)(3) .
Insulin is a peptide hormone produced by beta cells of the pancreas (2) .It hastwo essential functions: (1) insulin stimulates glucoseuptake and lipid synthesis; (2) insulin inhibits the breakdown of lipids, proteins and glycogen, and also inhibits the glucose biosynthesis pathway (gluconeogenesis) (4)(5)(6) .There are two main types of diabetes, type-1 and type-2, and also what is termed gestational diabetes that affects females during pregnancy.Type-1 diabetes is also known as insulin-dependent diabetes (7) .
In type-2 diabetes, the body does not produce enough insulin for proper functioning orthe cells do not react to insulin (insulin resistance) (8) .As type 2 diabetes is a progressivedisease, intensification of therapy is normally required over time, traditional treatmentalgorithms oftenfail to address the progressive nature of the disease.Furthermore, current therapeutic agents may also be associated with wide range of various effects: increased risk of hypoglycemia (sulphonylureas and insulin), weight gain (sulphonylureas, thiazolidinediones and insulin), and gastrointestinal intolerance (metformin), which representbarriers to maximum glycemic control (9)(10)(11) .One of the current therapies is Alphaglucosidase inhibitors.α-Glucosidase is thekey enzyme which catalyzes the final step in the digestion of carbohydrates in mammalians.Hence, α -glucosidase inhibitorscan suppress the liberation of D-glucose of oligosaccharides and disaccharidesfrom dietary complex carbohydrates and prolong glucoseabsorption, resulting in decrease post-prandial plasma glucose levels and retard post-prandial hyperglycemia (12,13) .Consequently,α -glucosidase inhibitors havebeen approved for clinical use in the management of type 2 diabetes,as well as the treatment of obesitysuch as acarboseandmiglitol (14,15) .However it was found that phthalimide, tetrachlorophthalimide derivatives exhibited potent α -glucosidase inhibition and the structure activity relationship studies show the following: 1.A phthalimide or tetrachlorophthalimide moiety connected to a variously substituted phenyl ring by an alkyl chain shows promising alpha glucosidase inhibitory activity (Scheme 1). 2. Studies revealed the importance of the distance between the phthalimidering and the phenyl moiety.3. Presence of an electron withdrawing group (NO2, CF3 etc.) at the (R3) position was more potent.4.Tetrachlorophthalimideskeleton is a useful non-sugar-type sugar mimic pharmacophore; it is characterized by highlipophilicity which could influence their pharmacokinetic propertiesand biological activity (16) .

Materials and Methods
All chemicals and solvents used during synthesis were of analytical grade and used without further purification.Completion of reactions and the purity of compounds were ascertained by A. Thin-layer chromatography (TLC), using Silica gel GF254 (type 60) pre-coated Aluminum sheets, Merck (Germany) and the eluent used is 1.Chloroform : methanol (85:15) 2. Glacial acetic acid: ethyl Acetate: methanol (0.1:3:1)to run TLC.B. High performance liquid chromatography was performed at the Lebanese university / Lebanon (PF4370) for the final compounds in order to ensure complete purity of compounds.Melting points were determined using Stuart SMP3 melting point apparatus in open capillary tubes, and are uncorrected.Fourier-Transform Infrared spectroscopy (FTIR), (KBr disc) (υ,cm -1 ) were recorded using (Biotech engineering management FTIR-600, UK) at College of Science-Al-Mustansiriya University, and the College of Pharmacy-Al-Mustansiriya University.Furthermore, The elemental microanalysis of the synthesized compounds was done using (Elementar vario MICRO cube instrument ,Germany) in the University of Mustansiriya-College of Pharmacy.
Proton-NMR spectra and ( 13 C NMR): were recorded on (Bruker, Germany NMR Spectra 300 MHz, Avance III 300 spectrometer) with tetramethylsilane (TMS) as an internal standard, dimethyl sulphoxide used as a solvent for samples measurement, (δ=ppm) and coupling constant in Hertz, which was run in (Lebanese University)-Lebanon.

Synthesis of N,N-phthaloyl-acid chloride (compounds3a, 3band 3c)
N,N-phthaloyl glycine (Compound2a),or N,N-tetra chloro phthaloyl glycine ( compound 2b) or N,N-tetra chloro phthaloylBOC Dap OH(compound 2c) (5mmol) was placed in a 50 mL round-bottom flask and then thionyl chloride (5 mL) was added.Thionyl chloride was added dropwise over a period of 15 min.with cooling on ice bath.The mixture was refluxed for 8 hrs at 65 °C with continuous stirring and monitored by evolution of HCl gas (which is detected by changing the color of litmus paper into reddish when placed on the top of condenser) and changing the color of the solution.The reaction are often promoted by the addition of a drop of dimethylformamide (DMF) (20) .The excess of thionyl chloride was removed under reduced pressure and the residue was re-dissolving in dry dichloromethane (10 ml )and was reevaporated to give an oily residue.The resulting acyl chloride (Compounds 3a, 3band 3c) wereused directly for the next step (21) .

Synthesis of N-phthaloyl-amino acid amides ( compounds 5a-o.)
A solution of one amine derivatives(5fluorouracil, or 4-chloroaniline, or 4bromoaniline, or 2-aminothiazole, or Pyrrolidine) (compounds 4a-e, 5.5 mmol) were mixed with dry dichloromethane ( 15 ml) except for 4a and 4d using mixture of 5 ml DMF and 10 ml dichloromethane , then triethylamine (5 mmol, 0.5 ml) was added drop wise with stirring for 20 min.on ice bath and then, freshly prepared acid chloride of either N,N-phthaloyl-(Compounds 3a,3band 3c)were slowly dropped for 50 min.with continuous stirring on an ice bath, and stirring was continued at room temperature overnight.The reaction can be accelerated with a catalytic amount (2-3 drops) of pyridine, or N, N-dimethylaminopyridine (DMAP) (22).Solvents were removed under reduced pressure by using rotary evaporator.The resulting solid product was re-dissolved in ethyl acetate (10 ml) and washed with 5 % aqueous solution of sodium bicarbonate (20 ml), 5% HCl (20 ml) and distilled water (20 ml) and then dried over anhydrous magnesium sulphate[compounds 5a-o] (18,19) .

Deprotection of tert butyloxycarbonyl (N-Boc) of compounds (5k-5o)
The respective peptide (compounds 5k-5o) was dissolved in CH2Cl2 or in CH2Cl2:CH3OH 9:1 (depending on solubility) and cooled to 0 °C.Trifluoroacetic acid (equal volume as the solvent) (10 ml) was added and the solution was allowed to warm to room temperature.After stirring at room temperature until starting material was consumed (TLC monitoring), the solution was concentrated in vacuum.The solution washed with saturated aqueous NaHCO3 solution (CH3OH was added to assure solubility of the peptide), water, and brine solution.The combined organic layers were dry over MgSO4, filtered, and evaporated in vacuum to yield the crude product in quantitative yield.In case of remaining protected peptide, the procedure was repeated.The reaction mixture was evaporated in vacuum and evaporated several times after adding CH2Cl2 to remove residual TFA and give the product in quantitative yield (23)(24)(25) .

In vitro evaluation of α-glucosidase inhibitory activity
The-glucosidase activity of some tested compounds (5a, 5f and6a) was determined according to the method described by Kim et al., using-glucosidase enzyme extracted from Saccharomyces bacteria.The substrate solution p-nitrophenol glucopyranoside (pNPG) was prepared in 20mM phosphate buffer, and pH 6.9. 100 L of glucosidase (1.0U/mL) was pre incubated with 50 L of the different concentrations of the test compound (in DMSO) for 10min.Then 50 L of 3.0mM (pNPG) as a substrate dissolved in 20mM phosphate buffer (pH 6.9) was then added to start the reaction.The reaction mixture was incubated at 37°C for 20min and stopped by adding 2mL of 0.1MNa2CO3.The glucosidase activity was determined by measuring the yellow-colored para nitrophenol released from pNPG at 400 nm using UV-Visible spectrophotometer.The results were expressed as percentage of the blank control.
Acarbose uses as positive control, Concentrations of extracts resulting in 50% inhibition of enzyme activity (IC50) were determined graphically are shown in Figures (2-4) (26) .

Spectral data and chemistry
The synthesis of our compounds (intermediates and end products) is depicted in scheme 1.The physical properties and the spectroscopic (IR, 1H-NMR) data of the synthesized compounds: White solid ;yield 85.6%;Melting point: 267-270°C; IR (KBr), (υ,cm -1 ): 3132 NH str.v. of secondary amide of 5-fu, 3066 (C-H) Str  The fusion of amino acids with phthalic anhydride is a widely used methodology.For some amino acids good yields are obtained, but in some cases the conditions used are so drastic that racemization occurs.Furthermore, amino acids with functionalized side chains failed to give the desired phthaloylated products.The extent of this racemization was limited by performing the reactions in boiling solvents and the presence of bases such as triethylamine.In such reactions, the medium should be kept neutral by slow distillation of the base and the water formed to allow cyclization of the intermediate phthalamic acids.Under prolonged heating, however, partial hydrolysis of the phthaloyl derivative to the intermediate phthalamic acid was sometimes observed (27) .During the last years, considerable attention have been devoted to the creation of αglucosidase inhibitors, which can be classified into sugar mimicking and non-sugar types according to their structural features (28- 30) .Sugar-mimicking α-glucosidase inhibitors have been extensively studied, including: Acarbose,miglitol and voglibosehave been clinically used to inhibit small intestinal αglucoside enzymes, such as α-glucosidase and glucoamylase (31) .The synthesized compounds (5a, 5f, 6a) IC50 values: 5.18, 4.6, 7.3 respectively accordingly these compounds have excellent alphaglucosidase inhibitory activity in comparison with standard compound acarbose (IC50= 817.38 ± 6.27 M), These results could be attributed to generation new binding site with a hydrophobic pocket in the active site of enzyme, the secondary amine in 5-flouro uracil ring bind by an ionic bond, aromatic rings by hydrophobic bonds while oxygen, nitrogen, chlorine and fluoride atoms bind through hydrogen bonds.

Conclusion
The