Relationships among the herbicide and functional sites of acetohydroxy acid synthase from Chlorella emersonii

The properties of acetohydroxy acid synthase (AHAS, EC 4.1.3.18) from wild-type Chlorella emersonii (var. Emersonii, CCAP-211/11n) and two spontaneous sulfometuron methyl (SMM)-resistant mutants were examined. The AHAS from both mutants was resistant to SMM and cross-resistant to imazapyr (IM) and the triazolopyrimidine sulfonanilide herbicide XRD-498 (TP). The more-SMM-resistant mutant had AHAS with altered catalytic parameters (K _m, specificity), but unchanged sensitivity to the feedback inhibitors valine and leucine. The second mutant enzyme was less sensitive to the feedback inhibitors, but had otherwise unchanged kinetic parameters. Inhibition-competition experiments indicated that the three herbicides (SMM, IM, TP) bind in a mutually exclusive manner, but that valine can bind simultaneously with SMM or TP. The three herbicide classes apparently bind to closely overlapping sites. We suggest that the results with C. emersonii and other organisms can all be explained if there are separate binding sites for herbicides, feedback inhibitors and substrates.Abbreviations AHAS acetohydroxy acid synthase - AL acetolactate - AHB acetohydroxybutyrate - IM imazapyr - TP triazolopyrimidine sulfonanilide herbicide XRD-498 - R enzyme specificity - SMM sulfometuron methyl This research was supported in part by the United States — Israel Binational Science Foundation (BSF), Jerusalem, Israel (Grant 86-00205) and the Fund for Basic Research, Israel Academy of Sciences.     

Synthesis, characterization, crystal structures and in vitro antistaphylococcal activity of organotin(IV) derivatives with 5,7-disubstituted-1,2,4-triazolo[1,5-a]pyrimidine

New organotin(IV) complexes of 5,7-ditertbutyl-1,2,4-triazolo[1,5-a]pyrimidine (dbtp) and 5,7-diphenyl-1,2,4-triazolo[1,5-a]pyrimidine (dptp) with 1:1 and/or 1:2 stoichiometry were synthesized and investigated by X-ray diffraction, FT-IR and ¹¹⁹Sn Mössbauer in the solid state and by ¹H and ¹³C NMR spectroscopy, in solution. Moreover, the crystal and molecular structures of Et₂SnCl₂(dbtp)₂ and Ph₂SnCl₂(EtOH)₂(dptp)₂ are reported. The complexes contain hexacoordinated tin atoms: in Et₂SnCl₂(dbtp)₂ two 5,7-ditertbutyl-1,2,4-triazolo[1,5-a]pyrimidine molecules coordinate classically the tin atom through N(3) atom and the coordination around the tin atom shows a skew trapezoidal structure with axial ethyl groups. In Ph₂SnCl₂(EtOH)₂(dptp)₂ two ethanol molecules coordinate tin through the oxygen atom and the 5,7-diphenyl-1,2,4-triazolo[1,5-a]pyrimidine molecules are not directly bound to the metal center but strictly H-bonded, through N(3), to the OH group of the ethanol moieties; Ph₂SnCl₂(EtOH)₂(dptp)₂ has an all-trans structure and the C-Sn-C fragment is linear. On the basis of Mössbauer data, the 1:2 diorganotin(IV) complexes are advanced to have the same structure of Et₂SnCl₂(dbtp)₂, while Me₂SnCl₂(dptp)₂ to have a regular all-trans octahedral structure. A distorted cis-R₂ trigonal bipyramidal structure is assigned to 1:1 diorganotin(IV) complexes. The in vitro antibacterial activities of the synthesized complexes have been tested against a group of reference pathogen micro-organisms and some of them resulted active with MIC values of 5 μg/mL, most of all against staphylococcal strains, which shows their inhibitory effect.     

1,2,4-triazolo[4,3-a]pyrimidines: a new kind of ligands. Structure of the silver(I) dimer with the 7-oxo derivative

This paper describes the silver dinuclear complex [Ag₂L₂(NO₃)₂] · 2H₂O, where L represents the bridging ligand 7,8-dihydro-7-oxo-1,2,4-triazolo[4,3-a]pyrimidine, this being the first example of a coordination compound of a 1,2,4-triazolo[4,3-a]pyrimidine derivative. As a difference with the most studied 1,2,4-triazolo[1,5-a]pyrimidine derivatives, the coordination takes place through the contiguous nitrogen atoms of the triazole ring, closing a six member Ag₂N₄ core with a higher intermetallic distance, 3.4791(3) Å. Linear coordination of silver is not possible in this geometry, so flat trigonal coordination involving also the nitrate counteranion is found instead.     

Coordination chemistry of substituted [1,2,4]triazolo[1,5-a]pyrimidines with first-row transition-metal ions: Synthesis, spectroscopy and single-crystal structure analysis

A number of new coordination compounds with transition-metal salts and triazole-based heterocyclic ligands is described. The ligands used are disubstituted [1,2,4]triazolo[1,5-a]pyrimidines, with as substituents: ethyl, methyl and phenyl, and in addition a 2-methylthio-dimethyl ligand was used (sdmtp). To determine the structures of the coordination compounds in a number of cases 3D crystal structure determinations have been carried out, i.e. for [Fe(NCS)₂(detp)₃(H₂O)], [Co(NCS)₂(sdmtp)₂(H₂O)], [ZnBr₂(fmtp)₂], [Ni(NCS)₂(detp)₃(CH₃OH)] and [Fe(NCS)₂(fmtp)₂(H₂O)₂](fmtp). The latter compound is quite unusual as it contains an uncoordinated fmtp ligand in the crystal lattice with special packing features. The ligands and the coordination compounds have been further characterized by NMR, IR and LF spectra, as well as by C, H, N element analyses. The coordination around the metal varies from 4 (Zn), via 5 (Co) to 6 (for Ni and Fe).     

Solvent-dependent 2D-coordination polymers of Cu(I) containing a bridging triazolopyrimidine ligand

Two 2D-polymers of Cu(I), [Cu₂(μ-tp)(CH₃CN)(μ-I)(μ₃-I)]_n (1) and [Cu₂(μ-tp)(μ₃-I)₂]_n (2), both obtained from the reaction between copper iodide and 1,2,4-triazolo[1,5-a]pyrimidine (tp) in the presence of KI are described. While in compound 1, tp acts as bridging ligand via N1 and N3 between chair-like [Cu₄I₄] units, in compound 2, tp moieties are placed at both sides of a [Cu_nI_n] kinked layer, displaying also a bridging mode but, in this case, through its atoms N3 and N4. These structural differences between both compounds seem to be due to the solvent of crystallization, being acetonitrile for 1 and water for 2. These polymers are the first examples of Cu(I) compounds based on the nucleobase-analog ligand tp.     

Design and synthesis of triazolopyrimidine acylsulfonamides as novel anti-mycobacterial leads acting through inhibition of acetohydroxyacid synthase

Novel triazolopyrimidine acylsulfonamides class of antimycobacterial agents, which are mycobacterial acetohydroxyacid synthase (AHAS) inhibitors were designed by hybridization of known AHAS inhibitors such as sulfonyl urea and triazolopyrimidine sulfonamides. This Letter describes the synthesis and SAR studies of this class of molecules by variation of two parts of the molecule, the phenyl and triazolopyrimidine rings. SAR study describes optimisation of enzyme potency, whole cell potency and evidence of mechanism of action.     

Design,synthesis and evaluation of photoactivatable derivatives of microtubule (MT)-active [1,2,4]triazolo[1,5-a]pyrimidines

The [1,2,4]triazolo[1,5-a]pyrimidines comprise a promising class of non-naturally occurring microtubule (MT)-active compounds. Prior studies revealed that different triazolopyrimidine substitutions can yield molecules that either promote MT stabilization or disrupt MT integrity. These differences can have important ramifications in the therapeutic applications of triazolopyrimidines and suggest that different analogues may exhibit different binding modes within the same site or possibly interact with tubulin/MTs at alternative binding sites. To help discern these possibilities, a series of photoactivatable triazolopyrimidine congeners was designed, synthesized and evaluated in cellular assays with the goal of identifying candidate probes for photoaffinity labeling experiments. These studies led to the identification of different derivatives that incorporate a diazirine ring in the amine substituent at position 7 of the triazolopyrimidine heterocycle, resulting in molecules that either promote stabilization of MTs or disrupt MT integrity. These photoactivatable candidate probes hold promise to investigate the mode of action of MT-active triazolopyrimidines.     

Naphthalene-triazolopyrimidine hybrid compounds as potential multifunctional anti-Alzheimer’s agents

In an attempt to construct potential anti-Alzheimer’s agents Naphthalene-triazolopyrimidine hybrids were synthesized and screened in vitro against the two cholinesterases (ChE)s, amyloid β aggregation and for antioxidation activity. Single-crystal X-ray crystallography was utilized for crystal structure determination of one of the compounds. In vitro study of compounds revealed that most of the compounds are capable of inhibiting acetylcholinesterase and Butyrylcholinesterase activity. Particularly, the compounds 4e and 4d exhibited IC₅₀ values ranging from 8.6 to 14 nM against AChE lower than the standard drug Donepezil (IC₅₀ 49 nM). Best result was found for compound 4e with IC₅₀ of 8.6 nM (for AChE) and 150 nM (for BuChE). Selectivity upto that of Donepezil and even more was observed for 4a, 4c and 4h. Investigation by electron microscopy, transmission electron microscopy and ThT fluorescence assay unveils the fact that synthesized hybrids exhibit amyloid β self-aggregation inhibition. The compounds 4i and 4j revealed highest inhibitory potential, 85.46% and 72.77% at 50 μM respectively; above the standard Aβ disaggregating agent, Curcumin. Their antioxidation profile was also analyzed. Studies from DPPH free radical scavenging assay and ORAC assay depicts molecules to possess low antioxidation profile. Results suggest that triazolopyrimidines are potential candidate for Acetylcholinesterase (AChE), Butyrylcholinesterase (BuChE), and amyloid β aggregation inhibition. In silico ADMET profiling indicates drug-like properties with a very low toxic influence. Such synthesized compounds provide a strong vision for further development of potential anti-Alzheimer’s agents.     

New copper(II), nickel(II) and zinc(II) complexes with 1,2,4-triazolo[1,5-a]pyrimidines and the chelating ligand 1,3-propanediamine: An unexpected coordination behavior for the 7-amine-derivative

Five new metal complexes with the metal ions Cu(II), Ni(II) and Zn(II) and containing 1,2,4-triazolo[1,5-a]pyrimidine derivatives and 1,3-propanediamine (tn) are described. The structural morphology of these coordination compounds depends on the triazolopyrimidine derivative used, being mononuclear for 5,7-dimethyl-1,2,4-triazolo[1,5-a]pyrimidine (dmtp) and 5-methyl-1,2,4-triazolo[1,5-a]pyrimidin-7(4H)-one (HmtpO), and 1D-polymeric for 7-amine-1,2,4-triazolo[1,5-a]pyrimidine (7atp). In the 7atp case, this ligand does not coordinate through N3 atom, as expected, but through N1, N4 and N71 in a bridging fashion. This unexpected coordination mode seems to be induced by the stability of the polynuclear metal complex in presence of tn ligand. All isolated metal complexes have been characterized by single-crystal X-ray diffraction, IR and UV-Vis spectroscopies, and EPR measurements. Moreover, luminescence measurements have been carried out for 7atp ligand and its polynuclear complex with Zn(II).     

The discovery of potent,orally bioavailable pyrazolo and triazolopyrimidine CXCR2 receptor antagonists

A hit-to-lead optimisation programme was carried out on the Novartis archive screening hit, pyrazolopyrimidine 2-methyl-5-((phenylthio)methyl)pyrazolo[1,5-a]pyrimidin-7-ol 1, resulting in the discovery of CXCR2 receptor antagonist 2-benzyl-5-(((2,3-difluorophenyl)thio)methyl)-[1,2,4]triazolo[1,5-a]pyrimidin-7-ol 14. The SAR was investigated by systematic variation of the pendant thiol, alkyl and pyrimidinol groups. Replacement of the pyrazolopyrimidine core with a triazolo alternative led to a dual series of antagonists with favourable biological and pharmacokinetic properties.