Preformulation Studies of Zidovudine Derivatives: Acid Dissociation Constants, Differential Scanning Calorimetry, Thermogravimetry, X-Ray Powder Diffractometry and Aqueous Stability Studies

As part as of the preformulation studies of new 5′-OH derivatives of zidovudine, compounds 2–6, their acid dissociation constants, Differential Scanning Calorimetry (DSC) and Thermogravimetry (TG) curves, X-Ray Powder diffractograms and aqueous stability are reported. A sensitive technique such as differential scanning potentiometry was used to determine the pKa constants of the above mentioned compounds. In addition, pKa values were calculated from theoretical methods, and no significant differences with those of experimental ones were observed. X-Ray Powder Diffractometry data demonstrated that compounds 2–4 were crystalline while 5 and 6 were amorphous. DSC analysis indicated that all of them presented an exothermic decomposition peak above 150 °C which is accompanied by a weight loss in the respective TG curves. The stability of these compounds in aqueous medium at different pH values was investigated, using a validated High Performance Liquid Chromatography (HPLC) method, which demonstrated to be rapid, selective, sensitive, accurate and stability-indicating. Good recovery, linearity and precision were also achieved. For all compounds the aqueous hydrolysis followed a pseudo-first-order kinetics, depending on pH and the union existing between AZT and the associate moiety. The hydrolysis was catalyzed by hydroxide ion in the 7.4–13.2 pH range, while all compounds exhibited pH-independent stability from acidic to neutral media (pHs 1.0–7.4)

Stability indicating MLC method for three novel deriviatives of zidovudine in aqueous and simulated gastric and intestinal fluids.

This work studies the stability of three new anti-HIV agents which were obtained by the association of zidovudine (AZT) with different amino acids, such as leucine (AZT-Leu) and valine (AZT-Val), and one with an acid group (AZT-Ac). Before commercialisation, their stability in different matrices – simulated gastric fluid (SGF, pH 1.2) and simulated intestinal fluid (SIF, pH 6.8), both as the USP 32 Guideline indicates, and buffers (pH 1.2 and 6.8) – must be studied. To this end, a new stability-indicating micellar liquid chromatography (MLC) method has been optimised and validated. Measurements were based on the disappearance of reagents and the appearance of the only degradation product (AZT). This optimised and validated method used a C18 column and a mobile phase containing 0.05 M sodium dodecyl sulphate–1% (v/v)1-butanol–0.01 M NaH2PO4 (pH 3.0) at 30 °C, and a flow rate of 1 mL min−1. Under these conditions, retention times were 1.4, 3.6, 6.3 and 9.5 min for AZT-Ac, AZT, AZT-Val and AZT-Leu, respectively. Calibrations better than 0.9995, intra- and inter-day precisions below 1.08% and good recoveries (94.47–116.52%) and robustness (RSD less that 1.08%) were obtained and were adequate to analyse the four compounds. Finally, this MLC method was applied to achieve stability studies which resulted in the evidence that all the compounds followed a pseudo-first-order kinetics, and in the determination of their kinetic constants and half-life time. A reference method, applied in the same studies, validated the MLC method reported herein

Synthesis, biological evaluation and molecular modeling of 4,6-diarylpyrimidines and diarylbenzenes as novel non-nucleosides HIV-1 reverse transcriptase inhibitors

A series of novel 4,6-diarylpyrimidines (4,6-DAPY) and diarylbenzenes (DABE) compounds were synthesized and evaluated as inhibitors of human immunodeficiency virus type-1 (HIV-1). Among them, the most potent HIV-1 inhibitors were 8b, 8d, 14b and 18 (EC(50) = 0.049, 0.381, 0.599 and 0.398 μM, respectively), with HIV-1 inhibitory activity improved or similar to nevirapine (NVP, EC(50) = 0.097 μM) and delavirdine (DEV, EC(50) = 0.55 μM). The other compounds displayed moderate activity (8c, EC(50) = 5.25 μM) or were inactive (8a and 14a) against HIV-1 replication. Molecular modeling studies were performed with the synthesized compounds in complex with the wild-type reverse transcriptase (RT). A correlation was found between the anti-HIV activity and the electrostatic energy of interaction with Lys101 residue. These findings enrich the SAR of these Non-Nucleoside Reverse Transcriptase Inhibitors (NNRTIs) families.status: publishe