Design, synthesis, and evaluation of bromo-retrochalcone derivatives as protein tyrosine phosphatase 1B inhibitors

A series of bromo-retrochalcones was designed, synthesized and evaluated as PTP1B inhibitors based on licochalcone A and E. Compounds 6, 12, 13, 14, 25, 36, 37, 39, and 41 showed potent inhibitory effects against PTP1B, and compound 37, the most potent among the series, had an IC₅₀ value of 1.9 μM, about two-fold better than that of the positive control, ursolic acid.     

Synthesis, characterization, and protein tyrosine phosphatases inhibition activities of oxovanadium(IV) complexes with Schiff base and polypyridyl derivatives

Seven new mixed-ligand vanadyl complexes, [V^IVO(5-Br-SAA)(NN)] and [V^IVO(2-OH-NAA)(NN)] (1-7) (5-Br-SAA for 5-bromosalicylidene anthranilic acid, 2-OH-NAA for 2-hydroxy-1-naphthaldehyde anthranilic acid and NN for N,N′-donor heterocyclic base, namely, 2,2′-bipyridine (bpy, 1 and 5), 1,10-phenanthroline (phen, 2 and 6), dipyrido[3,2-d:2′,3′-f]quinoxaline (dpq, 3 and 7), dipyrido[3,2-a:2′,3′-c]phenazine (dppz, 4)), were synthesized and characterized. X-ray crystal structure of [V^IVO(5-Br-SAA)(phen)] revealed a distorted octahedral geometry with the Schiff base ligand coordinated in a tridentate ONO-fashion and the phenanthroline ligand in a bidentate fashion. Density-functional theory (DFT) calculations suggest a similar structure and the same coordination mode for all the other oxovanadium complexes synthesized. Biochemical assays demonstrate that the mixed-ligand oxovanadium(IV) complexes are potent inhibitors of protein tyrosine phosphatase 1B (PTP1B), with IC₅₀ values approximately 41-75 nM. Kinetics assays suggest that the complexes inhibit PTP1B in a competitive manner. Notably, they had moderate selectivity of PTP1B over T-cell protein tyrosine phosphatase (TCPTP) (about 2-fold) and good selectivity over Src homology phosphatase 1 (SHP-1) (about 4∼7-fold). Thus, these mixed-ligand complexes represent a promising class of PTP1B inhibitors for future development as anti-diabetic agents.     

Tubulin photoaffinity labeling study with a plinabulin chemical probe possessing a biotin tag at the oxazole

A new bioactive photoaffinity probe KPU-252-B1 (4) possessing a biotin tag on the oxazole ring of a potent plinabulin derivative KPU-244 (2) was synthesized via the Cu^I-catalyzed Huisgen’s cycloaddition reaction to understand the precise binding mode of the diketopiperazine-based anti-microtubule agent plinabulin on tubulin. Probe 4 showed significant binding affinity toward tubulin and cytotoxicity against an HT-29 cells. A photoaffinity labeling study suggested that probe 4 specifically recognizes tubulin at a binding site that binds plinabulin or colchicine, most likely near or at the colchicine binding site, which is located at the interfacial region formed by ??-and ??-tubulin association. The results also demonstrated that probe 4 may serve as a useful plinabulin chemical probe to investigate the molecular mechanism by which anti-microtubule diketopiperazine derivatives operate.     

Study of the preferred modification sites of the quinone methide intermediate resulting from the latent trapping device of the activity probes for hydrolases

Use of activity probes has been demonstrated to be a powerful tool in modern chemical proteomic study. Previously we have designed and synthesized a series of mechanism-based activity probes that utilized quinone methide chemistry. Here, we characterized the trend of chemical reactivity for the reactive quinone methide intermediate 3 (QM-3) resulting from the latent trapping device. In a competition assay, the labeling of PTP1B by probe 1a was blocked by externally added cysteine without affecting the catalytic activity of the enzyme. Further sequencing analysis on the trypsin-digested peptides of probe 1a-labeled PTP1B using tandem mass spectrometry revealed that all six cysteine residues of PTP1B are capable of being modified by probe 1a. These results indicated that the sulfhydryl group of cysteine residue is the preferred nucleophile for the reactive QM-3. Our finding provides the first example in understanding the preferred amino acid residues modified by the reactive QM-3, which is also the key structural unit responsible for forming covalent bonds in many biochemical applications.     

Synthesis and characterization of the ligand based on benzoxazole and its transition metal complexes: DNA-binding and antitumor activity

A new ligand 2-((2-((benzo[d]oxazol-2-yl)methoxy)phenoxy)methyl)benzoxazole (L) and its four transition metal complexes M(NO₃)₂L (M = Cu, Co, Ni, Zn), have been synthesized and investigated. The single crystal structures of the complexes show that all of them have similar molecular structure and the ligand exhibits good coplanarity after coordination with the metal ions. Further investigation of DNA binding indicates that both the ligand L and the complexes can bond to DNA by intercalation mode, and the latter possesses much stronger binding affinity. Antitumor activity of these compounds tested on the four cancer cell lines, follows the order: Cu-L > Ni-L ≈ Co-L > Zn-L ? L, which are thought to be related with their DNA-binding affinity.     

Selective activation of SHP2 activity by cisplatin revealed by a novel chemical probe-based assay

Src homology-2 (SH2) domain-containing phosphatase 2 (SHP2) is known to participate in several different signaling pathways to mediate cell growth, survival, migration, and differentiation. However, due to the lack of proper analytical tools, it is unclear whether the phosphatase activity of SHP2 is activated in most studies. We have previously developed an activity-based probe LCL2 that formed covalent linkage with catalytically active protein tyrosine phosphatases (PTPs). Here, by combining LCL2 with a SHP2 specific antibody, we established an assay system that enables the direct monitoring of SHP2 activity upon cisplatin treatment of cancer cells. The protocol is advantageous over conventional colorimetric or in-gel PTP assays as it is specific and does not require the use of radioisotope reagents. Using this assay, we found SHP2 activity was selectively activated by cisplatin. Moreover, the activation of SHP2 appeared to be specific for cisplatin as other DNA damage agents failed to activate the activity. Although the role of SHP2 activation by cisplatin treatments is still unclear to us, our results provide the first direct evidence for the activation of SHP2 during cisplatin treatments. More importantly, the concept of using activity-based probe in conjunction with target-specific antibodies could be extended to other enzyme classes.     

Guest releasing from solution to solid-state triggered by cyclomaltohexaose (α-cyclodextrin) aggregation

Supramolecuar aggregations 1 and 2 were prepared by complexing cyclomaltohexaose with two azodipyridine isomers: 4,4′-azodipyridine and 2,2′-azodipyridine, and their binding abilities and assembly behaviors were investigated comprehensively by X-ray crystallography, 2D NMR spectroscopy, and isothermal titration calorimetry. In solution, 1:1 host-guest complexation is generally assumed, whereas in the solid state, a 2:1 stoichiometry is observed. Crystal structures reveal that channel-type aggregation exists in complex 1, while a layer-type manner is the dominant packing mode in complex 2. The disparity of nitrogen atom position leads to the different binding modes and further affects the aggregation types in complexes 1 and 2.     

Design of a potent, soluble glucokinase activator with increased pharmacokinetic half-life

The continued optimization of a series of glucokinase activators is described, including attempts to understand the interplay between molecular structure and the composite parameter of unbound clearance. These studies resulted in the discovery of a new scaffold for glucokinase activators and further exploration of this scaffold led to the identification of GKA60. GKA60 maintains an excellent balance of potency and physical properties whilst possessing a significantly different, but complimentary, pre-clinical pharmacokinetic profile compared with the previously disclosed compound GKA50.     

1,3-Dipolar cycloaddition to the FeSC fragment 20. Preparation and properties of carbonyliron complexes of di-thiooxamide. Reactivity of the mononuclear (di-thiooxamide)Fe(CO)3 towards dimethyl acetylenedicarboxylate

Reaction of Fe₂(CO)₉ at room temperature in THF with the di-thiooxamides (L), SC{N(R,R′)}C{(R,R′)N}S [R=Me, R′-R′=(CH₂)₂ (a); R=H, R′=ⁱPr (b); R=H, R′=iPr (c), R=H, R′=benzyl (d); R=H, R′=H (e)], results for ligands a-d initially in the formation of the mononuclear σ-S, σ-S′ chelate complexes Fe(CO)₃(L) (7a-d), which could be isolated in case of 7a and 7d. Under the reaction conditions, complexes 7a-d react further with [Fe(CO)₄] fragments to give three types of Fe₂(CO)₆(L) complexes (8a-d) in high yields, depending on the di-thiooxamide ligand used together with traces of the known complex S₂Fe₃(CO)₉ (14). The molecular structures of these complexes have been established by the single crystal X-ray diffraction determinations of 8a, 8b and 8d. In the reaction with ligand e the corresponding complex 7e was not detected and the well-known complexes 14 and S₂Fe₃(CO)₉ (15) were isolated in low yield. In situ prepared 7a reacts in a slow reaction with 1 equiv. of dimethyl acetylene dicarboxylate in a 1,3-dipolar cycloaddition reaction to give the stable initial ferra [2.2.1] bicyclic complex 10a in 60% yield. In complex 10a an additional Fe(CO)₄ fragment is coordinated to the sulfido sulfur atom of the cycloadded FeSC fragment. When a toluene solution of 10a is heated to 50 °C it loses two terminal CO ligands to give the binuclear FeFe bonded complex 11a in almost quantitative yield. The molecular structures of 10a and 11a have been confirmed by single crystal X-ray diffraction. Reaction of 7d at room temperature with 2 equiv. of dimethyl acetylene dicarboxylate results in the mononuclear complex 12d in 5% yield. The molecular structure of 12b has been established by single crystal X-ray diffraction and comprises a tetra dentate ligand with two ferra-sulpha cyclobutene, and a ferra-disulpha cyclopentene moiety. When the reaction is performed at 60 °C a low yield of 2,3,4,5-thiophene tetramethyl tertracarboxylate is obtained besides complex 12d.     

Antitumor agents 279. Structure-activity relationship and in vivo studies of novel 2-(furan-2-yl)naphthalen-1-ol (FNO) analogs as potent and selective anti-breast cancer agents

In our ongoing modification study of neo-tanshinlactone (1), we discovered 2-(furan-2-yl)naphthalen-1-ol (FNO) derivatives 3 and 4 as a new class of anti-tumor agents. To explore structure-activity relationships (SAR) of this scaffold, 18 new analogs, 6-12 and 14-24, were designed and synthesized. The C11-esters 7 and 12 displayed broad anti-tumor activity (ED₅₀ 1.1-4.3 μg/mL against seven cancer cell lines), while C11-hydroxymethyl 14 showed unique selectivity against the SKBR-3 breast cancer cell line (ED₅₀ 0.73 μg/mL). Compounds 15 and 22 displayed potent and selective anti-breast tumor activity (ED₅₀ 1.7 and 0.85 μg/mL, respectively, against MDA-MB-231). The SAR results demonstrated that the substitutions from the ring-opened lactone ring C of 1 are critical to the anti-tumor potency as well as the apparent tumor-tissue type selectivity. Treatment with 3 in Brca1^f11/f11p53^f5&6/f5&6Cre^c mice models significantly inhibited the proliferation of mammary epithelial cells and branching of mammary glands.     

Pyrazoline based MAO inhibitors: synthesis, biological evaluation and SAR studies

Twenty-two pyrazoline derivatives were synthesized and tested for their human MAO (hMAO) inhibitory activity. Twelve molecules with unsubstituted ring A and substituted ring C (5-16) were found to be potent inhibitors of hMAO-A isoform with SI_MAO-A in the order 10³ and 10⁴. Ten molecules with unsubstituted ring A and without ring C (21-30), in which eight molecules (21, 23-26, and 28-30) were selective for hMAO-A, one for hMAO-B (22) and the other one non-selective (27). Presence of ring C increases potency as well as SI towards hMAO-A; however its absence decreases both potency and SI towards hMAO-A and hMAO-B.     

Dopamine release and molecular modeling study of some coumarin derivatives

4-aryl-2-amino-6-(4-hydroxy-2-oxo-2H-chromen-3-yl)-pyridin-3-carbonitrile (1), 4-aryl-2-oxo-6-(4-hydroxy-2-oxo-2H-chromen-3-yl)-pyridin-3-carbonitriles (2a-2c), 3-(6-aryl-1,2,5,6- tetrahydro-2-thioxopyrimidin-4-yl)-4-hydroxy-2H-chromen-2-one (3a, 3b) and pyrazol-3-yl-4-hydroxycoumarin derivatives (4a-4c, 5, 6a, 6b, 7a, 7b, and 8a-8c) were prepared in order to measure their % change dopamine release in comparison to amphetamine as reference, using PC-12 cells in different concentrations. In addition, the molecular modeling study of the compounds into 3BHH receptor was also demonstrated. The calculated inhibition constant (k_i) implemented in the AutoDock program revealed identical correlation with the experimental results to that obtained binding free energy (ΔG_b) as both parameters revealed reasonable correlation coefficients (R²) being 0.51 involving 10 compounds; (1, 2b, 2c, 3a, 3b, 4a, 4b, 6a, and 8c).     

Novel analogues of ketamine and phencyclidine as NMDA receptor antagonists

The identification of structurally novel analogues of ketamine and phencyclidine (PCP), as NMDA receptor antagonists, with low to moderate potency at GluN2A and GluN2B receptors is discussed. In particular, some examples, such as compounds 6 and 10, shows decreased calculated lipophilicity, when compared to PCP, while retaining moderate activity. Moreover, the germinal aryl amino substituted lactam ring, as exemplified in compounds 7-10 and 11-13, constitutes a novel scaffold with potential application in the design of biologically active compounds.     

Structural requirements of (E)-6-benzylidene-4a-methyl-4,4a,5,6,7,8-hexahydronaphthalen-2(3H)-one derivatives as novel melanogenesis inhibitors

Chalcone type compound 1a ((E)-6′-benzylidene-4a′-methyl-4′,4a′,7′,8′-tetrahydro-3′H-spiro[[1,3]dithiolane-2,2′-naphthalen]-5′(6′H)-one) was discovered as an potent inhibitor in melanogenesis. To define its structure-activity relationship, a series of analogs 1b-n, dithiolane truncated 2a-b and ring A removed 3a-e were prepared and evaluated. The electron donating substitution on the phenyl ring (ring C) rather than an electron withdrawing group and dithiolane motif of 1 are needed for the activity enhancement. The scaffold containing both rings A and B associated with α,β-unsaturated system connected to phenyl of 1 was essential for antimelanogenesis.     

Synthesis, structure, DNA binding and cleavage properties of ternary amino acid Schiff base-phen/bipy Cu(II) complexes

Ternary Cu(II) complexes [Cu(II)(saltrp)(B)] (1,2), (saltrp = salicylidene tryptophan, B = 1,10 phenathroline (1) or 2,2′ bipyridine (2)) were synthesized and characterized. Complex 2 was structurally characterized by single crystal X-ray crystallography. The molecular structure shows a distorted square pyramidal coordination geometry (CuN₃O₂) in which the ONO donor Schiff base is bonded to the Cu(II) in the basal plane. The N,N donor heterocyclic base displays an axial-equatorial binding mode. CT-DNA binding studies revealed that the complexes show good binding propensity (Intrinsic binding constant, K_b = 3.32 × 10⁵ M⁻¹ for 1 and K_b = 3.10 × 10⁵ M⁻¹ for 2). The catalytic role of these complexes in the oxidative and hydrolytic cleavage of DNA was studied in detail. Complex 1 binds and cleaves DNA more efficiently as compared to 2. From the kinetic experiments, rate constants for the hydrolysis of phosphodiester bond of DNA backbone were determined as 1.94 h⁻¹ and 1.05 h⁻¹ for 1 and 2 respectively. It amounts to (2.93-5.41) × 10⁷ fold rate enhancement compared to uncatalyzed double stranded DNA, which is impressive as compared to related Cu(II) Schiff base complexes.     

Exploring new near-infrared fluorescent disulfide-based cyclic RGD peptide analogs for potential integrin-targeted optical imaging

We synthesized disulfide-based cyclic RGD pentapeptides bearing a near-infrared fluorescent dye (cypate), represented by cypate-c(CRGDC) (1) for integrin-targeted optical imaging. These compounds were compared with the traditional lactam-based cyclic RGD counterpart, cypate-c(RGDfK) (2). Molecular modeling suggests that the binding affinity of 2 to integrin α_vβ₃ is an order of magnitude higher than that of 1. This was confirmed experimentally, which further showed that substitution of Gly with Pro, Val and Tyr in 1 remarkably hampered the α_vβ₃ binding. Interestingly, cell microscopy with A549 cells showed that 1 exhibited higher cellular staining than 2. These results indicate that factors other than receptor binding affinity to α_vβ₃ dimeric proteins mediate cellular uptake. Consequently, 1 and its analogs may serve as valuable molecular probes for investigating the selectivity and specificity of integrin targeting by optical imaging.     

Triterpenoid saponins from Echinopsis macrogona (Cactaceae)

Triterpene saponins, pachanosides C1, E1, F1 and G1 (1-4), and bridgesides A1, C1, C2, D1, D2, E1 and E2 (5-11) were isolated from Echinopsis macrogona. Compounds 1-4 were saponins with pachanane type triterpene saponins, while the others (5-11) were oleanane type triterpene saponins. While the aglycones of 2-4 and 8-11 were hitherto unknown, the structure of pachanol C was revised in this paper. Their structures were elucidated on the basis of chemical and physicochemical evidence.     

Methyl or ethyl makes the difference: Synthesis and solid-state structure of 9,10-dialkyl-9,10-dihydro-9,10-digallaanthracenes

The donor-free 9,10-dialkyl-9,10-dihydro-9,10-digallaanthracenes 1 (alkyl: methyl) and 2 (alkyl: ethyl) were prepared by reaction of 1,2-di(chloromercurio)benzene with the corresponding trialkylgallium and isolated as colourless air- and moisture sensitive crystalline compounds. In the solid-state structure of 1, two slightly different monomers 1A and 1B are found, which form a dimer 1A?1B held together by “medium” strong gallium arene π-interactions. Further weak π-interactions between 1A and 1A and 1B and 1B constitute a one-dimensional coordination polymer containing strands of the composition [?(1A?1B)?(1B?1A)?]_n. In contrast, compound 2 crystallizes in the form of distinct molecular units without any further intermolecular π-interactions. The molecular units possess D_2d symmetry and are built by strong π-interactions between two digallaanthracene monomers. Two symmetrical aryl group bridges between two gallium atoms are observed for the first time in the subunits of 2. By addition of a Lewis-base (THF, Pyridine) to 2, a monomeric planar digallaanthracene framework is restored, as proven by an X-ray crystal structure analysis of 2 · 2Py. The different structures of 1 and 2 are explained on the basis of steric effects.     

Synthesis of 5-thiodidehydropyranylcytosine derivatives as potential anti-HIV agents

As a part of our ongoing efforts to identify new anti-HIV agents, a 5′-thiopyrano-nucleoside derivative 4, designed based on 4′-thioD4C 1 and cyclohexenylnucleoside 3, was synthesized. The dihydrothiopyran skeleton of 4 was constructed by the ring closing metathesis of 21 which was synthesized from but-2-yne-1,4-diol. After converting the protecting group from MOM to TBS followed by oxidation, a Pummerer-type thioglycosylation reaction of 24 with persilylated uracil gave the desired 5-thiodihydrothiopyranyluracils 25 and 26 as a mixture of anomers. The conversion of 25 to a cytosine derivative and subsequent deprotection gave a 5-thiodidehydropyranosylcytosine derivative 4 in good yield. The anti-HIV activity of 4 was also evaluated.     

From “naked” copper(II) ions and asymmetric macrocyclic complex linkers with a monodentate top and a bidentate top to molecular rectangle and infinite molecular rectangle strands

A molecular rectangle [Cu{CuL¹(NO₃)}(H₂O)(NO₃)]₂ (1) and two infinite molecular rectangle strands {[Cu{CuL¹(NO₃)}₂] · 2H₂O}_∞ (2) and [Cu{CuL²(ClO₄)}₂]_∞ (3) were prepared by reaction of “naked” Cu(II) ions with macrocyclic complex ligands CuL¹ for 1 and 2 and CuL² for 3 in metal-to-ligand molar ratios of 1:1, 1:2 and 1:2, respectively. L¹ and L² denote the dianions of diethyl 5,6,7,8,15,16-hexahydro-6,7-dioxodibenzo[1,4,8,11]tetraazacyclotetradecine-13,18-dicarboxylate and diethyl 5,6,7,8,15,16-hexahydro-15-methyl-6,7-dioxodibenzo[1,4,8,11]tetraazacyclotetradecine-13,18-dicarboxylate, respectively. The structures of 1-3 were determined by X-ray single-crystal analyses. CuL¹ in 1 and 2 and CuL² in 3 act as angular linkers with a monodentate coordination top and a bidentate one between two Cu(II) nodes to enclose the molecular rectangle of 1 and the rectangular subunits of 2 and 3. The angular shape, the monodentate top plus bidentate top coordination mode and the self-complementarity for π?π interactions of the macrocyclic complex linkers, the ratio between the reactants and the octahedral coordination geometry of the naked Cu(II) ions jointly determined the interesting structures of metallocyclophane 1 and 1D double chain coordination polymers 2 and 3. The cavities of the rectangular molecules of 1 are arranged into infinite strands so that parallel channels occur in the crystal. The molecules of 2 and 3 all pack parallel in the crystals.