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This article investigates the aqueous solubility of the poorly soluble drug candesartan cilexetil (CC) in the presence of poly(amidoamine) (PAMAM) dendrimers. The effect of variables such as concentration, generation size (G2-G4), and surface groups (NH, COOH and TRIS) of PAMAMs on the aqueous solubility of CC was studied. A two-factor factorial (3 × 3) ANOVA design was used to study the effect of generation size and surface functional group of the PAMAMs. The results showed that the aqueous solubility of CC in the presence of carboxyl and TRIS-terminated PAMAMs was higher than those of amine-terminated PAMAMs, and the effect of surface functional group of the PAMAMs on the aqueous solubility of CC was dependent on the generation size (p < 0.05). The sequence of the observed solubility fold enhancement due to PAMAMs was G4.COOH (8378)>G3.COOH (3456)>G4.TRIS (2362)>G2.COOH (1013)>G3.TRIS (749)>G2.TRIS (293)>G4.NH (91)>G3.NH (50)>G2.NH (37). The CC-PAMAM dendrimer inclusion complexes were characterized by UV-Vis, attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) and differential thermal analysis (DTA) techniques. Regarding the results of these techniques, improvement in the solubility of CC is expected primarily through the intermolecular hydrogen bonding between the drug and internal tertiary and surface functional groups of the studied PAMAMs.

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This study is the first report describing the microwave-assisted synthesis (MAS) of poly(amido amine) (PAMAM) dendrimers with TRIS surface functional groups (PAMAM-TRIS). Six PAMAM-TRIS dendrimers were synthesized using both newly developed conventional and microwave methods. Five of them are novel. Three different cores, one polymeric Jeffamine® T-403 and two monomeric, ethylenediamine and diethylenetriamine, were used in the syntheses. All the reactions were monitored by attenuated total reflectance (ATR). It was observed that microwave reactions proceeded 3.5 to 4.0 times faster than conventional reactions. Therefore, a fast, easy and one-pot MAS of six different water-soluble PAMAM-TRIS dendrimers was accomplished with high (90-96%) yields in short (110-140 min) reaction times and under mild reaction conditions, using methanol as solvent. The other ester terminated half generation precursor PAMAM (PAMAM-OCH 3 ) dendrimers used for the synthesis of the PAMAM-TRIS dendrimers were obtained by utilizing conventional and microwave methods together. For the purification of all the PAMAM dendrimers, a liquid phase polymer-based retention (LPR) technique was used. The PAMAM-TRIS dendrimers were characterized by 1 H NMR, 13 C NMR, ATR (IR), EA, potentiometric and spectroscopic titrations. Furthermore, Cu(II)-PAMAM-TRIS dendrimer complexes were prepared and characterized by UV-Vis spectroscopy. The synthesized PAMAM-TRIS dendrimers can be considered as new drug carrier systems and should find use in widespread application fields, especially in future pharmaceutical and catalytic studies but also in other fields.

Sulfamethoxazole (SMZ) is a sulfonamide and used widely in the treatment of bacteriostatic and urinary tract infections with trimethoprim as an antibiotic. The problem with SMZ is its poor water solubility, therefore, low bioavailability in clinical applications. In this study, we synthesized new-generation Tris(2-aminoethyl)amine (TREN)-cored amine (NH), Tris(hydroxymethyl)aminomethane (TRIS), and carboxyl (COOH) terminated different generations T2-T4 poly(amidoamine) PAMAM dendrimers. Synthesized PAMAMs were characterized by H NMR,C NMR, ATR-FTIR, spectroscopic titrations, and evaluated as potential solubility enhancers and drug carriers of sulfonamides by taking SMZ as a model drug. The effect of concentration, generation, and surface groups of PAMAMs on the solubility of SMZ was also investigated. Results showed that the solubility of SMZ improved significantly with an increasing generation size (T2-T4) and PAMAM dendrimer concentration (0-2 mM). The role of PAMAMs in the solubility enhancement of SMZ was in the order of T4.NH > T4.COOH > T3.NH > T4.TRIS > T2.NH > T3.COOH > T3.TRIS > T2.COOH > T2.TRIS, and in the ranges of 5- to 45-fold with maximum SMZ loading 7 to 61 mole/mole per PAMAM dendrimer molecule. In vitro release studies demonstrated that SMZ-PAMAM dendrimer complexes at the end of 2-h drug release (16-26%) was considerable slower than pure SMZ (38.8%).

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