Synthesis of [14C]‐ and [13C6]‐labeled potent HIV non‐nucleoside reverse transcriptase inhibitor

5,11‐Dihydro‐11‐ethyl‐5‐methyl‐8‐{2‐{(1‐oxido‐4‐quinolinyl)oxy}ethyl}‐6H‐dipyrido[3,2‐b:2′,3′‐e][1,4]diazepin‐6‐one, (1), labeled with carbon‐14 in the quinoline–benzene ring, in one of the pyridine rings of the dipyridodiazepinone tricyclic moiety, and in the side chain, was prepared in three different syntheses with specific activities ranging from 44 to 47 mCi/mmol (1.63–1.75 GBq/mmol). In the first synthesis, 5,11‐dihydro‐11‐ethyl‐8‐(2‐hydroxyethyl)‐5‐methyl‐6H‐dipyrido[3,2‐b:2′,3′‐e][1,4]diazepin‐6‐one (2) was coupled to 4‐hydroxyquinoline, [benzene‐¹⁴C(U)]‐, using Mitsunobu's reaction conditions, followed by the oxidation of the quinoline nitrogen with 3‐chloroperoxybenzoic acid to give ([¹⁴C]‐(1a)) in 43% radiochemical yield. Second, 3‐amino‐2‐chloropyridine, [2,6‐¹⁴C]‐, was used to prepare 8‐bromo‐5,11‐dihydro‐11‐ethyl‐5‐methyl‐6H‐dipyrido[3,2‐b:2′,3′‐e][1,4]diazepin‐6‐one (8), and then Stille coupled to allyl(tributyl)tin followed by ozonolysis of the terminal double bond and in situ reduction of the resulting aldehyde to alcohol (10). Mitsunobu etherification and oxidation as seen before gave ([¹⁴C]‐(1b)) in eight steps and in 11% radiochemical yield. Finally, carbon‐14 potassium cyanide was used to prepare isopropyl cyanoacetate (12), which was used to transform bromide (8) to labeled aryl acetic acid (13) under palladium catalysis. Trihydroborane reduction of the acid gave alcohol (14) labeled in the side chain, which was used as described above to prepare ([¹⁴C]‐(1c)) in 4.3% radiochemical yield. The radiochemical purities of these compounds were determined by radio‐HPLC and radio‐TLC to be more than 98%. To prepare [¹³C₆]‐(1), [¹³C₆]‐4‐hydroxyquinoline was prepared from [¹³C₆]‐aniline and then coupled to (2) and oxidized as seen before. Copyright © 2008 John Wiley & Sons, Ltd.     

Structure‐based drug design and in vitro testing reveal new inhibitors of enoyl‐acyl carrier protein reductases

The need for new antibacterial agents is increasingly becoming of great importance as bacterial resistance to current drugs is quickly spreading. Enoyl‐acyl carrier protein reductases (FabI) are important enzymes for fatty acid biosynthesis in bacteria and other micro‐organisms. In this project, we conducted structure‐based virtual screening against the FabI enzyme, and accordingly, 37 compounds were selected for experimental testing. Interestingly, five compounds were able to demonstrate antimicrobial effect with variable inhibition activity against various strains of bacteria and fungi. Minimum inhibitory concentrations of the active compounds were determined and showed to be in low to medium micromolar range. Subsequently, enzyme inhibition assay was carried out for our five antimicrobial hits to confirm their biological target and determine their IC₅₀ values. Three of these tested compounds exhibited inhibition activity for the FabI enzyme where our best hit MN02 had an IC₅₀ value of 7.8 μM. Furthermore, MN02 is a small bisphenolic compound that is predicted to have all required features to firmly bind with the target enzyme. To sum up, hits discovered in this work can act as a good starting point for the future development of new and potent antimicrobial agents.     

Pharmacokinetic interaction between efavirenz and dual protease inhibitors in healthy volunteers

The combination of efavirenz with HIV-1 protease inhibitors (PI) results in complex interactions secondary to mixed induction and inhibition of oxidative metabolism. ACTG A5043 was a prospective, open-label, controlled, two-period, multiple-dose study with 55 healthy volunteers. The objective of the present study was to evaluate the potential pharmacokinetic interaction between efavirenz and dual PIs. The subjects received a daily dose of 600 mg efavirenz for 10 days with amprenavir 600 mg twice daily added at day 11 and were randomized to receive nelfinavir, indinavir, ritonavir, saquinavir, or no second PI on days 15-21. Intensive pharmacokinetic studies were conducted on day 14 and 21. Efavirenz plasma concentrations were fit to candidate models using weighted non-linear regression. The disposition of efavirenz was described by a linear two-compartment model with first order absorption following a fitted lag time. Apparent clearance (CLt/F), volume of distribution at steady state (Vss/F), inter-compartmental clearance, and the central and peripheral volume of distribution were estimated. The mean CLt/F and Vss/F of efavirenz were 0.126 l/h/kg and 4.412 l/kg, respectively. Both AUC and CLt/F of efavirenz remained unchanged after 7 days of dual PI dosing. The mean Vss/F of efavirenz increased an average of 89% across arms, ranging from 52% (nelfinavir) to 115% (indinavir) relative to efavirenz with amprenavir alone. Increases were also observed in Vp/F after the addition of nelfinavir, indinavir, ritonavir and saquinavir by 85%, 170%, 162% and 111%, respectively. In conclusion, concomitant administration of dual PIs is unlikely to have any clinically significant effect on the pharmacokinetics of CYP2B6 substrates in general or oral efavirenz specifically.     

Molecular insights into trypanothione reductase‐inhibitor interaction: A structure‐based review

Information on how small molecules bind to the target enzyme has the potential to impact immensely on how medicinal chemists go about antiparasitic drug discovery. In this review, for the first time, we intend to make an assessment of the structural aspects of trypanothione reductase as drug target, and its complexes with several reversible drugs from the Protein Data Bank (PDB). We attempt to reveal the mechanism of these interactions by careful accounting of the X‐ray structures and their possible roles in biological activity to treat Trypanosomatidae diseases. We focus on some of the outstanding findings from structures that are relevant to anti‐trypanocidal drug discovery. We also review new interesting compounds that have appeared in the literature based on these X‐ray structures.

     

Molecular Modeling,Synthesis, and Anti‐HIV Activity of Novel Isoindolinedione Analogues as Potent Non‐nucleoside Reverse Transcriptase Inhibitors

Different isoindolinedione derivatives bearing imine, amide, thioamide, and sulfonamide linkages have been designed in silico using discovery studio software (BIOVIA, San Diego, CA, USA), synthesized, and evaluated for their anti‐HIV activity. SAR studies revealed that the linkages in these molecules did affect their anti‐HIV activity and the molecules having sulfonamide linkages were the most potent HIV‐RT inhibitors as the S=O bonds of the sulfonamide moiety interacted with Lys103 (NH or carbonyl or both) and Pro236; the NH part of the sulfonamide linkage formed bond with carbonyl of Lys101. blood–brain barrier (BBB) plots were also studied, and it was found that all the designed molecules have potential to cross BBB, a very vital criteria for anti‐HIV drugs. In vitro screening was performed using HIV‐1 strain IIIB in MT‐4 cells using the MTT assay, and it was seen that some of these molecules were effective inhibitors of HIV‐1 replication at nanomolar concentration with selectivity indices ranging from 33.75 to 73.33 under in vitro conditions. Some of these molecules have shown good anti‐HIV activity at 3–4 nm concentrations. These derivatives have potential to be developed as lead molecules effective against HIV‐1. Novel isoindolinedione derivatives as probable NNRTIs have been synthesized and characterized. Some of these molecules have shown good anti‐HIV activity at 3–4 nm concentrations.     

Structure‐based approaches for the design of benzimidazole‐2‐carbamate derivatives as tubulin polymerization inhibitors

Microtubules are highly dynamic assemblies of α/β‐tubulin heterodimers whose polymerization inhibition is among one of the most successful approaches for anticancer drug development. Overexpression of the class I (βI) and class III (βIII) β‐tubulin isotypes in breast and lung cancers and the highly expressed class VI (βVI) β‐tubulin isotype in normal blood cells have increased the interest for designing specific tubulin‐binding anticancer therapies. To this end, we employed our previously proposed model of the β‐tubulin–nocodazole complex, supported by the recently determined X‐ray structure, to identify the fundamental structural differences between β‐tubulin isotypes. Moreover, we employed docking and molecular dynamics (MD) simulations to determine the binding mode of a series of benzimidazole‐2‐carbamete (BzC) derivatives in the βI‐, βIII‐, and βVI‐tubulin isotypes. Our results demonstrate that Ala198 in the βVI isotype reduces the affinity of BzCs, explaining the low bone marrow toxicity for nocodazole. Additionally, no significant differences in the binding modes between βI‐ and βIII‐BzC complexes were observed; however, Ser239 in the βIII isotype might be associated with the low affinity of BzCs to this isotype. Finally, our study provides insight into the β‐tubulin–BzC interaction features essential for the development of more selective and less toxic anticancer therapeutics.     

Structure‐based design,synthesis, and pharmacologic evaluation tf peptide RGS4 inhibitors

Abstract: Regulators of G‐protein signaling (RGS) proteins form a multifunctional signaling family. A key role of RGS proteins is binding to the G‐protein Gα‐subunit and acting as GTPase‐activating proteins (GAPs), thereby rapidly terminating G protein‐coupled receptor (GPCR) signaling. Using the published RGS4–G_iα1 X‐ray structure we have designed and synthesized a series of cyclic peptides, modeled on the G_iα Switch I region, that inhibit RGS4 GAP activity. These compounds should prove useful for elucidating RGS‐mediated activity and serve as a starting point for the development of a novel class of therapeutic agent.