Design and synthesis of tetraol derivatives of 1,12-dicarba-closo-dodecaborane as non-secosteroidal vitamin D analogs

Vitamin D receptor (VDR), a nuclear receptor for 1α,25-dihydroxyvitamin D₃ (1α,25(OH)₂D₃, 1), is a promising target for multiple clinical applications. We recently developed non-secosteroidal VDR ligands based on a carbon-containing boron cluster, 1,12-dicarba-closo-dodecaborane (p-carborane), and examined the binding of one of them to VDR by means of crystallographic analysis. Here, we utilized that X-ray structure to design novel p-carborane-based tetraol-type vitamin D analogs, and we examined the biological activities of the synthesized compounds. Structure–activity relationship study revealed that introduction of an ω-hydroxyalkoxy functionality enhanced the biological activity, and the configuration of the substituent significantly influenced the potency. Among the synthesized compounds, 4-hydroxybutoxy derivative 9a exhibited the most potent activity, which was equal to that of the secosteroidal vitamin D analog, 19-nor-1α,25-dihydroxyvitamin D₃ (2).     

Identification of a new selective dopamine D4 receptor ligand

The dopamine D₄ receptor has been shown to play key roles in certain CNS pathologies including addiction to cigarette smoking. Thus, selective D₄ ligands may be useful in treating some of these conditions. Previous studies in our laboratory have indicated that the piperazine analog of haloperidol exhibits selective and increased affinity to the DAD₄ receptor subtype, in comparison to its piperidine analog. This led to further exploration of the piperazine moiety to identify new agents that are selective at the D₄ receptor. Compound 27 (K_iD₄ = 0.84 nM) was the most potent of the compounds tested. However, it only had moderate selectivity for the D₄ receptor. Compound 28 (K_iD₄ = 3.9 nM) while not as potent, was more discriminatory for the D₄ receptor subtype. In fact, compound 28 has little or no binding affinity to any of the other four DA receptor subtypes. In addition, of the 23 CNS receptors evaluated, only two, 5HT_1AR and 5HT_2BR, have binding affinity constants better than 100 nM (K_i <100 nM). Compound 28 is a potentially useful D₄-selective ligand for probing disease treatments involving the D₄ receptor, such as assisting smoking cessation, reversing cognitive deficits in schizophrenia and treating erectile dysfunction. Thus, further optimization, functional characterization and evaluation in animal models may be warranted.     

Bisindolylmethane thiosemicarbazides as potential inhibitors of urease: Synthesis and molecular modeling studies

Bisindolylmethane thiosemicarbazides 1-18 were synthesized, characterized by ¹H NMR and ESI MS and evaluated for urease inhibitory potential. All analogs showed outstanding urease inhibitory potentials with IC₅₀ values ranging between 0.14?±?0.01 to 18.50?±?0.90?μM when compared with the standard inhibitor thiourea having IC₅₀ value 21.25?±?0.90?μM. Among the series, analog 9 (0.14?±?0.01?μM) with di-chloro substitution on phenyl ring was identified as the most potent inhibitor of urease. The structure activity relationship has been also established on the basis of binding interactions of the active analogs. These binding interactions were identified by molecular docking studies.     

A series of nonsecosteroidal vitamin D receptor agonists for osteoporosis therapy

In an extension of our study on gamma hydroxy carboxylic acid analogs, we explored a series of nonsecosteroidal vitamin D receptor (VDR) agonists in which 1,3-diol of 1,25(OH)₂D₃ had been replaced by aryl acetic acid. These analogs showed very potent activity in vitro compared with 1,25(OH)₂D₃. An X-ray analysis of 8d showed that the inserted phenyl ring well mimicked the folded methylene linker of the gamma hydroxy carboxylic acid moiety but the carboxylic acid of 8d interacted with VDR in a different manner from gamma hydroxy carboxylic acids. Through our in vivo screening in an osteoporosis rat model using immature rats, we identified a potent active vitamin D₃ analog, compound 7e. In mature rats of the same model, compound 7e also showed good PK profiling and excellent ability to prevent bone mineral density loss without severe hypercalcemia. Our nonsecosteroidal VDR agonist 7e (CH5036249) could be a possible new drug candidate for treating osteoporosis in human.     

Synthesis and characterization of selective dopamine D2 receptor antagonists. 2. Azaindole,benzofuran, and benzothiophene analogs of L-741,626

A series of indole, 7-azaindole, benzofuran, and benzothiophene compounds have been prepared and evaluated for affinity at D_2-like dopamine receptors. These compounds share structural elements with the classical D_2-like dopamine receptor antagonists haloperidol, N-methylspiperone and benperidol. Two new compounds, 4-(4-iodophenyl)-1-((4-methoxy-1H-indol-3-yl)methyl)piperidin-4-ol (6) and 4-(4-iodophenyl)-1-((5-methoxy-1H-indol-3-yl)methyl)piperidin-4-ol (7), were found to have high affinity to and selectivity for D₂ versus D₃ receptors. Changing the aromatic ring system from an indole to other heteroaromatic ring systems reduced the D₂ binding affinity and the D₂ versus D₃ selectivity.     

Muscarinic agonist, (±)-quinuclidin-3-yl-(4-fluorophenethyl)(phenyl)carbamate: High affinity,but low subtype selectivity for human M1 – M5 muscarinic acetylcholine receptors

Novel quinuclidinyl N-phenylcarbamate analogs were synthesized, and binding affinities at M₁-M₅ muscarinic acetylcholine receptor (mAChR) subtypes were determined using Chinese hamster ovary (CHO) cell membranes stably expressing one specific subtype of human mAChR. Although not subtype selective, the lead analog (±)-quinuclidin-3-yl-(4-fluorophenethyl)(phenyl)carbamate (3c) exhibited the highest affinity (K_i?=?2.0, 13, 2.6, 2.2, 1.8?nM) at each of the M₁-M₅ mAChRs, respectively. Based on results from the [³H]dopamine release assay using rat striatal slices, 3c acted as an agonist at mAChRs. The effect of 3c was inhibited by the nonselective mAChR antagonist, scopolamine, and 3c augmented release evoked by oxotremorine. A potent analog from the same scaffold, (±)-quinuclidin-3-yl-(4-methoxyphenethyl)(phenyl)-carbamate (3b) exhibited the greatest selectivity (17-fold) at M₃ over M₂ mAChRs. These analogs could serve as leads for further discovery of novel subtype-selective muscarinic ligands with the goal of providing therapeutics for substance use disorders and chronic obstructive pulmonary disease.     

Complexation of NADH analogs with divalent metal ions: Dependence on the 3-substituent of 1-benzyl-1,4-dihydropyridines

In light of the critical role of divalent metal ions in the chemistry of coenzyme NADH analogs, complexation of 1-benzyl-3-substituted(X)-1,4-dihydropyridines (1, X=CONH₂; 2, X=CSNH₂; 3, X=COOCH₃; 4, X=COCH₃) with divalent metal ions (Mg²⁺, Zn²⁺, and Co²⁺) in dry acetonitrile was studied spectroscopically and kinetically. Presence of the metal ions causes red-shift of absorption band of NADH analogs and the rate retardation for the reaction between NADH analogs and N-methylacridinium ion. Analysis of the spectroscopic and kinetic data indicates that the NADH analogs form 1 : 1 complexes with the metal ions. The decreasing order of the magnitude of the association constants, K, is 1 2 4 3 for a given metal ion, and Mg²⁺ Zn²⁺ > Co²⁺ for a given NADH analog. The results strongly suggest that the primary binding site for the metal ions is the carbonyl oxygen (or thiocarbonyl sulfur) of the 3-substituent and that the amide nitrogen atom of the 3-substituent of 1 and 2 also ligates the metal ions, forming a bidentate structure and providing extra stability to the complexes of 1 and 2. Inhibition of reaction between NADH analogs and N-methylacridinium ion by the metal ions is attributed to inaccessibility of N-methylacridinium ion to the NADH analogs complexed with metal ions due to electrostatic repulsion.     

An analog of 1α,25-dihydroxy-19-norvitamin D3 with the 1α-hydroxy group fixed in the axial position lacks biological activity in vitro

The relationship between the A-ring chair conformation of vitamin D compounds and their ability to bind the vitamin D receptor (VDR) has long attracted the attention of many researchers. It was established that in the crystalline complexes of hVDRmt with the natural hormone, 1α,25-dihydroxyvitamin D₃ (1), and its side-chain analogs the vitamins exist in β-chair form with an equatorial orientation of 1α-OH. However, with all these ligands the interconversion between both A-ring forms would be possible in solution. In an attempt to verify the conformation of vitamin D compounds required for binding the VDR we prepared analog 4, characterized by the presence of an axial 1α-hydroxy group. Since the additional ring connecting 3β-oxygen and C-2 prevents A-ring conformational flexibility, the synthesized vitamin 4 can exist exclusively in the α-chair form. The geometrical isomer 5 with a free 3β-OH group was also obtained. The analog 5 binds very poorly to VDR, whereas the vitamin 4 is practically devoid of binding ability. Both compounds also show very low HL-60-differentiating activity. When tested in vivo in mice the analogs 4 and 5 exhibit significant calcemic responses with analog 4 showing more activity than analog 5.     

Design,synthesis, and biological activity of new endomorphin analogs with multi-site modifications

Endomorphin (EM)-1 and EM-2 are the most effective endogenous analgesics with efficient separation of analgesia from the risk of adverse effects. Poor metabolic stability and ineffective analgesia after peripheral administration were detrimental for the use of EMs as novel clinical analgesics. Therefore, here, we aimed to establish new EM analogs via introducing different bifunctional d-amino acids at position 2 of [(2-furyl)Map⁴]EMs. The combination of [(2-furyl)Map⁴]EMs with D-Arg² or D-Cit² yielded analogs with enhanced binding affinity to the μ-opioid receptor (MOR) and increased stability against enzymatic degradation (t_1/2 > 300 min). However, the agonistic activities of these analogs toward MOR were slightly reduced. Similar to morphine, peripheral administration of the analog [D-Cit², (2-furyl)Map⁴]EM-1 (10) significantly inhibited the pain behavior of mice in multiple pain models. In addition, this EM-1 analog was associated with reduced tolerance, less effect on gastrointestinal mobility, and no significant motor impairment. Compared to natural EMs, the EM analogs synthesized herein had enhanced metabolic stability, bioavailability, and analgesic properties.     

The utility of 1-[18F]fluoro-3-iodopropane for the synthesis of certain dopamine D-1 and benzodiazepine receptor radioligands

No-carrier-added (NCA) R(+)-7-chloro-8-hydroxy-3-(3′-[¹⁸F]fluoropropyl)-1-phenyl-2,3,4,5-tetrahydro-3-benzazepine (2b) (an analog of dopamine D-1 receptor ligand SCH 23390), ethyl 8-fluoro-5,6-dihydro-5-(3′-fluoropropyl)-6-oxo-4H-imidazo[1,5-a][1,4]benzodiazepine-3-carboxylate (4b) and 3′-[¹⁸F]fluoropropyl 8-fluoro-5,6-dihydro-5-methyl-6-oxo-4H-imidazo[1,5-a][1,4]benzodiazepine-3-carboxylate (6b) (analogs of the benzodiazepine RO 15-1788) were synthesized by alkylation of the corresponding nor-compound with NCA 1-[¹⁸F]fluoro-3-iodopropane in 10–15% yield (EOB) in ~110min and with a mass of 2–3nmol. Compound 2 is less potent (~ 12–14 times) than SCH 23390 in binding to rat striatal membranes in vitro. Compounds 2b, 4b and 6b exhibit no specific anatomical distribution to mouse brain. These results suggest that the substituent at position 3 of SCH 23390, and position 5 and carboxylate group of RO 15-1788 are critical determinants both of affinity and selectivity for receptor binding, and underscores the evaluation necessary when even minor changes (C1 to C3) are made in bioactive compounds.     

NMR studies of new arginine vasopressin analogs modified with α-2-indanylglycine enantiomers at position 2 bound to sodium dodecyl sulfate micelles

In this paper, we use NMR spectroscopy and molecular modeling to examine four new vasopressin analogs modified with α-2-indanylglycine (Igl) at position 2, [L-Igl²]AVP (I), [D-Igl²]AVP (II), [Mpa¹,L-Igl²]AVP (III) and [Mpa¹,D-Igl²]AVP (IV), embedded in a sodium dodecyl sulfate (SDS) micelle. All the analogs display antiuterotonic activity. In addition, the analogs with D-Igl reveal antipressor properties.Each analog exhibits the tendency to adopt β-turns at positions 2, 3 and/or 3, 4, which is characteristic of oxytocin-like peptides. Mutual arrangement of aromatic residues at positions 2 and 3 has been found to be crucial for binding antagonists with the OT and V_1a receptors. The orientation of the Gln⁴ side chain seems to be important for the V_1a receptor affinity. In each of the peptides studied, the Gln⁴ side chain is folded back over the ring moiety. However, it lies on the opposite face of the tocin moiety in analogs with L and D enantiomers of Igl.     

Derivatives of (R)-2-amino-5-methoxytetralin: Antagonists and inverse agonists at the dopamine D2a receptor

A series of N-arylmethyl substituted (R)-5-methoxy-2-(propylamino)tetralins has been prepared and evaluated for affinity and efficacy at dopamine (DA) D_2a receptors. The novel compounds appeared to be antagonists or inverse agonists. (R)-2-[(Benzyl)propylamino]-5-methoxytetralin (7) was characterized as a potent inverse agonists at DA D_2a receptors in a [³⁵S]GTPγS binding assay.     

Evaluation of N-phenyl homopiperazine analogs as potential dopamine D3 receptor selective ligands

A series of N-(2-methoxyphenyl)homopiperazine analogs was prepared and their affinities for dopamine D₂, D₃, and D₄ receptors were measured using competitive radioligand binding assays. Several ligands exhibited high binding affinity and selectivity for the D₃ dopamine receptor compared to the D₂ receptor subtype. Compounds 11a, 11b, 11c, 11f, 11j and 11k had K_i values ranging from 0.7 to 3.9 nM for the D₃ receptor with 30- to 170-fold selectivity for the D₃ versus D₂ receptor. Calculated log P values (log P = 2.6–3.6) are within the desired range for passive transport across the blood–brain barrier. When the binding and the intrinsic efficacy of these phenylhomopiperazines was compared to those of previously published phenylpiperazine analogues, it was found that (a) affinity at D₂ and D₃ dopamine receptors generally decreased, (b) the D₃ receptor binding selectivity (D₂:D₃ K_i value ratio) decreased and, (c) the intrinsic efficacy, measured using a forskolin-dependent adenylyl cyclase inhibition assay, generally increased.     

Synthesis and evaluation of novel azetidine analogs as potent inhibitors of vesicular [3H]dopamine uptake

Lobelane analogs that incorporate a central piperidine or pyrrolidine moiety have previously been reported by our group as potent inhibitors of VMAT2 function. Further central ring size reduction of the piperidine moiety in lobelane to a four-membered heterocyclic ring has been carried out in the current study to afford novel cis-and trans-azetidine analogs. These azetidine analogs (15a–15c and 22a–22c) potently inhibited [³H]dopamine (DA) uptake into isolated synaptic vesicles (K_i ? 66 nM). The cis-4-methoxy analog 22b was the most potent inhibitor (K_i = 24 nM), and was twofold more potent that either lobelane (2a, K_i = 45 nM) or norlobelane (2b, K_i = 43 nM). The trans-methylenedioxy analog, 15c (K_i = 31 nM), was equipotent with the cis-analog, 22b, in this assay. Thus, cis- and trans-azetidine analogs 22b and 15c represent potential leads in the discovery of new clinical candidates for the treatment of methamphetamine abuse.     

Synthesis, α-amylase inhibitory potential and molecular docking study of indole derivatives

In search of potent α-amylase inhibitor we have synthesized eighteen indole analogs (1–18), characterized by NMR and HR-EIMS and screened for α-amylase inhibitory activity. All analogs exhibited a variable degree of α-amylase inhibition with IC₅₀ values ranging between 2.031 ± 0.11 and 2.633 ± 0.05 μM when compared with standard acarbose having IC₅₀ values 1.927 ± 0.17 μM. All compounds showed good α-amylase inhibition. Compound 14 was found to be the most potent analog among the series. Structure-activity relationship has been established for all compounds mainly based on bringing about the difference of substituents on phenyl ring. To understand the binding interaction of the most active analogs molecular docking study was performed.     

Induction of calcium-binding protein in organ-cultured chick intestine by fluoro analogs of vitamin D3

Vitamin D-like steroids added to the culture medium induce a specific calcium-binding protein (CaBP) in embryonic chick duodenum maintained in organ culture. This system provides a biologically relevant assay, i.e., a physiological response in a principle target organ, for the study of the relative biopotency of vitamin D metabolites and analogs. A number of fluoro analogs of vitamin D₃ (D₃) and its metabolites were assayed in the present study. Analogs fluorinated in the lα position (1α-F-D₃) or in both the 1α and 25 positions (1α,25-F₂-D₃) were markedly more potent than vitamin D₃ itself although 1α,25-F₂-D₃ was only $\text{1}\text{7}\text{th}$ as potent as 1α-F-D₃. The 25-fluoro analog (25-F-D₃) was a very weak inducer; only $\text{1}\text{45}\text{th}$ as potent as vitamin D₃. The 25-fluoro analog of 1α-hydroxyvitamin D₃ (1α-OH-25-F-D₃) was less potent than its nonfluorinated counterpart. Although 25-fluorination reduced biopotency in all other analogs tested, 24R-OH-25-F-D₃ was about 15 times more potent than 24R,25-(OH)₂-D₃. Of considerable interest was the effect of difluorination at the 24-carbon position: both 24,24-F₂-25-OH-D₃ and 24,24-F₂-1α,25-(OH)₂-D₃ were about four times as potent as their nonfluorinated counterparts. The 24,24-F₂-1α,25-(OH)₂-D₃ is, therefore, the most potent vitamin D₃ analog yet tested in this system i.e., it is four times more potent than the most potent naturally occurring vitamin D₃ metabolite, 1α,25-(OH)₂-D₃.     

Identification of an N-oxide pyridine GW4064 analog as a potent FXR agonist

According to the docking studies and the analysis of a co-crystal structure of GW4064 with FXR, a series of 3-aryl heterocyclic isoxazole analogs were designed and synthesized. N-Oxide pyridine analog (7b) was identified as a promising FXR agonist with potent binding affinity and good efficacy, supporting our hypothesis that through an additional hydrogen bond interaction between the pyridine substituent of isoxazole analogs and Tyr373 and Ser336 of FXR, binding affinity and functional activity could be improved.