Synthetic access to diverse thiazetidines via a one-pot microwave assisted telescopic approach and their interaction with biomolecules

A one-pot microwave assisted telescopic approach is reported for the chemo-selective synthesis of substituted 1,3-thiazetidines using readily available 2-aminopyridines/pyrazines/pyrimidine, substituted isothiocyanates and 1,2-dihalomethanes. The procedure involves thiourea formation from 2-aminopyridines/pyrazines/pyrimidine with the substituted isothiocyanates followed by a base catalysed nucleophilic attack of the CS bond on the 1,2-dihalomethane. Subsequently, a cyclization reaction occurs to yield substituted 1,3-thiazetidines. These four membered strained ring systems are reported to possess broad substrate scope with high functional group tolerance. The above synthetic sequence for the formation of four membered heterocycles is proven to be a modular and straightforward approach. Further the mechanistic pathway for the formation of 1,3-thiazetidines was supported by computational evaluations and X-ray crystallography analyses. The relevance of these thiazetidines in biological applications is evaluated by studying their ability to bind bio-macromolecules like proteins and nucleic acids.

The Anti-Tumoral Potential of Phosphonate Analog of Sulforaphane in Zebrafish Xenograft Model

Isothiocyanates (ITCs) show strong activity against numerous human tumors. Five structurally diverse ITCs were tested in vivo using the zebrafish embryos 6 and 48 h post-fertilization (hpf). The survival rate, hatching time, and gross morphological changes were assessed 24, 48, and 72 h after treatment with all compounds in various doses (1-10 µM). As a result, we selected a phosphonate analog of sulforaphane (P-ITC; 1-3 µM) as a non-toxic treatment for zebrafish embryos, both 6 and 48 hpf. Furthermore, the in vivo anti-cancerogenic studies with selected 3 µM P-ITC were performed using a set of cell lines derived from the brain (U87), cervical (HeLa), and breast (MDA-MB-231) tumors. For the experiment, cells were labeled using red fluorescence dye Dil (1,1'-Dioctadecyl-3,3,3',3'-Tetramethylindocarbocyanine, 10 μg/mL) and injected into the hindbrain ventricle, yolk sac region and Cuvier duct of zebrafish embryos. The tumor size measurement after 48 h of treatment demonstrated the significant inhibition of cancer cell growth in all tested cases by P-ITC compared to the non-treated controls. Our studies provided evidence for P-ITC anti-cancerogenic properties with versatile activity against different cancer types. Additionally, P-ITC demonstrated the safety of use in the living organism at various stages of embryogenesis.

Synthesis of Isothiocyanates Using DMT/NMM/TsO- as a New Desulfurization Reagent

Thirty-three alkyl and aryl isothiocyanates, as well as isothiocyanate derivatives from esters of coded amino acids and from esters of unnatural amino acids (6-aminocaproic, 4-(aminomethyl)benzoic, and tranexamic acids), were synthesized with satisfactory or very good yields (25-97%). Synthesis was performed in a "one-pot", two-step procedure, in the presence of organic base (Et3N, DBU or NMM), and carbon disulfide via dithiocarbamates, with 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholinium toluene-4-sulfonate (DMT/NMM/TsO-) as a desulfurization reagent. For the synthesis of aliphatic and aromatic isothiocyanates, reactions were carried out in a microwave reactor, and selected alkyl isothiocyanates were also synthesized in aqueous medium with high yields (72-96%). Isothiocyanate derivatives of L- and D-amino acid methyl esters were synthesized, under conditions without microwave radiation assistance, with low racemization (er 99 > 1), and their absolute configuration was confirmed by circular dichroism. Isothiocyanate derivatives of natural and unnatural amino acids were evaluated for antibacterial activity on E. coli and S. aureus bacterial strains, where the most active was ITC 9e.

First Examples of H2S-Releasing Glycoconjugates: Stereoselective Synthesis and Anticancer Activities

H2S donors are currently emerging as promising therapeutic agents in a wide variety of pathologies, including tumors. Cancer cells are characterized by an enhanced uptake of sugars, such as glucose. Therefore, novel glycoconjugated H2S donors were synthesized so that high concentrations of H2S can be selectively achieved therein. Dithiolethione portions or isothiocyanate portions were selected for their well-known H2S-releasing properties in the presence of biological substrates. A synthetic procedure employing trichloroacetimidate glycosyl donors was applied to produce, in a stereoselective fashion, C1-glycoconjugates, whereas C6-glycoconjugates were obtained by a Mitsunobu-based transformation. The resulting molecules were then tested for their anticancer effects on human pancreas adenocarcinoma ascites metastasis cell line AsPC-1. The most potent inhibitors of cell viability (6aβ and 7b) proved to release H2S inside the AsPC-1 cells and to alter the basal cell cycle.

Differential Pharmacological Activities of Oxygen Numbers on the Sulfoxide Moiety of Wasabi Compound 6-(Methylsulfinyl) Hexyl Isothiocyanate in Human Oral Cancer Cells

6-(methylsulfinyl) hexyl isothiocyanate (6-MITC) is a naturally occurring compound isolated from Wasabia japonica (wasabi). The synthetic derivatives, 6-(methylsulfenyl) hexyl isothiocyanate (I7447) and 6-(methylsulfonyl) hexyl isothiocyanate (I7557), were derived from 6-MITC with the deletion and addition of oxygen, respectively. We aimed to evaluate the effect of these synthetic compounds on human oral cancer cells, SAS and OECM-1. All three compounds (I7447, 6-MITC, and I7557) inhibited the viability of SAS and OECM-1 cells using MTT assay. Morphological observations showed various proportions of mitotic arrest and apoptosis in cells treated with these compounds. Cell cycle analysis revealed relatively abundant G2/M arrest in 6-MITC and I7557-treated cells, whereas sub-G1 accumulation was found in I7447-treated cells. In using phosphorylated histone H3 as a marker for mitosis, the addition of 6-MITC and I7557 (excluding I7447) could be shown to arrest cells during mitosis. In contrast, I7447 induced more prominent apoptosis than the 6-MITC or I7557 compounds. The down-regulated expression of the phosphorylated form of CHK1 and Cdc25c was noted in 6-MITC and I7557-treated cells. I7557 could sensitize SAS cells to death by radiation. The wasabi compound, 6-MITC, and its chemical derivatives with different numbers of oxygen may have differential pharmacological effects on human oral cancer cells.

Differentiating Antiproliferative and Chemopreventive Modes of Activity for Electron-Deficient Aryl Isothiocyanates against Human MCF-7 Cells

The consumption of Brassica vegetables provides beneficial effects through organic isothiocyanates (ITCs), products of the enzymatic hydrolysis of glucosinolate secondary metabolites. The ITC l-sulforaphane (l-SFN) is the principle agent in broccoli that demonstrates several modes of anticancer action. While the anticancer properties of ITCs like l-SFN have been extensively studied and l-SFN has been the subject of multiple human clinical trials, the scope of this work has largely been limited to those derivatives found in nature. Previous studies have demonstrated that structural changes in an ITC can lead to marked differences in a compound's potency to 1) inhibit the growth of cancer cells, and 2) alter cellular transcriptional profiles. This study describes the preparation of a library of non-natural aryl ITCs and the development of a bifurcated screening approach to evaluate the dose- and time-dependence on antiproliferative and chemopreventive properties against human MCF-7 breast cancer cells. Antiproliferative effects were evaluated using a commercial MTS cell viability assay. Chemopreventive properties were evaluated using an antioxidant response element (ARE)-promoted luciferase reporter assay. The results of this study have led to the identification of 1) several key structure-activity relationships and 2) lead ITCs for continued development.

Therapeutic effects of isothiocyanate prodrugs on rheumatoid arthritis

Isothiocyanates 7a and 7b have poor stability and aqueous solubility. To address these problems, prodrugs 8a and 8b were synthesized. Prodrugs 8a and 8b were stable in HEPES buffer at pH 4.4, but released the active compounds 7a and 7b in HEPES buffer at pH 7.4 and in mouse plasma, respectively. Compound 8a and especially compound 8b showed anti-inflammatory effects. Compound 8b demonstrated significant efficacy in animal models of traumatic inflammation, acute inflammation and rheumatoid arthritis. Compound 8b also did not cause appreciable toxicity in mice after 5 weeks at a daily dose of 200 mg/kg.

Inactivation of protein tyrosine phosphatases by dietary isothiocyanates

Isothiocyanates are bioactive dietary phytochemicals that react readily with protein thiol groups. We find that isothiocyanates are time-dependent inactivators of cysteine-dependent protein tyrosine phosphatases (PTPs). Rate constants for the inactivation of PTP1B and SHP-2 by allyl isothiocyanate and sulforaphane range from 2 to 16 M(-1)s(-1). Results in the context of PTP1B are consistent with a mechanism involving covalent, yet reversible, modification of the enzyme's active site cysteine residue.

Syntheses, crystal structures, luminescent and magnetic properties of two molecular solids containing naphthylmethylene triphenylphosphinium cations and tetra(isothiocyanate)cobalt(II) dianion

The reaction of CoCl2 with the naphthalene methylated triphenylphosphinium bromide [n-NAPMeTPP]Br (n=1, 2) and KSCN, in a methanolic medium at ambient temperature, leads to the self-assembly formation of hybrid 2:1 organic-inorganic molecular solids, [1-NAPMeTPP]2[Co(NCS)4](1) and [2-NAPMeTPP]2[Co(NCS)4](2) ([NAPMeTPP](+)=(naphthylmethylene)(triphenyl)phosphinium), which have been characterized by elemental analyses, IR spectroscopy, UV-Vis spectra, ESI-MS, molar conductivity and single-crystal X-ray diffraction structural analyses. Compound 1 crystallizes in the orthorhombic space group Pna21, while 2 does in the monoclinic space group C2/c. The cations form a dimer through the weak intermolecular C-H⋯π interactions in 1 and π⋯π interaction in 2, while the anion and cation are linked by the C-H⋯S hydrogen bond in 1. Two molecular solids show dual functionalities: (1) the broad fluorescence emission around 400nm in the solid state at room temperature; (2) the weak antiferromagnetic coupling behavior.

Study of the cytotoxic effects of the new synthetic Isothiocyanate CM9 and its fullerene derivative on human T-leukemia cells

One important strategy to develop effective anticancer agents is based on natural products. Many active phytochemicals are in human clinical trials and have been used for a long time, alone and in association with conventional anticancer drugs, for the treatment of various types of cancers. A great number of in vitro, in vivo and clinical reports document the multi-target anticancer activities of isothiocyanates and of compounds characterized by a naphthalenetetracarboxylic diimide scaffold. In order to search for new anticancer agents with a better pharmaco-toxicological profile, we investigated hybrid compounds obtained by inserting isothiocyanate group(s) on a naphthalenetetracarboxylic diimide scaffold. Moreover, since water-soluble fullerene derivatives can cross cell membranes thus favoring the delivery of anticancer therapeutics, we explored the cytostatic and cytotoxic activity of hybrid compounds conjugated with fullerene. We studied their cytostatic and cytotoxic effects on a human T-lymphoblastoid cell line by using different flow cytometric assays. In order to better understand their pharmaco-toxicological potential, we also analyzed their genotoxicity. Our global results show that the synthesized compounds reduced significantly the viability of leukemia cells. However, the conjugation with a non-toxic vector did not increase their anticancer potential. This opens an interesting research pattern for certain fullerene properties.

Total synthesis of (-)-N-methylwelwitindolinone B isothiocyanate via a chlorinative oxabicycle ring-opening strategy

The first total synthesis of N-methylwelwitindolinone B isothiocyanate is reported. The route features several key steps, including a regio- and diastereoselective chlorinative oxabicycle ring-opening reaction to introduce the challenging alkyl chloride motif.

A one-pot approach to pyridyl isothiocyanates from amines

A one-pot preparation of pyridyl isothiocyanates (ITCs) from their corresponding amines has been developed. This method involves aqueous iron(III) chloride-mediated desulfurization of a dithiocarbamate salt that is generated in situ by treatment of an amine with carbon disulfide in the present of DABCO or sodium hydride. The choice of base is of decisive importance for the formation of the dithiocarbamate salts. This one-pot process works well for a wide range of pyridyl ITCs. Utilizing this protocol, some highly electron-deficient pyridyl and aryl ITCs are obtained in moderate to good yields.

Identifying and characterizing binding sites on the irreversible inhibition of human glutathione S-transferase P1-1 by S-thiocarbamoylation

Human glutathione S-transferase P1-1 (hGST P1-1) is involved in cell detoxification processes through the conjugation of its natural substrate, reduced glutathione (GSH), with xenobiotics. GSTs are known to be overexpressed in tumors, and naturally occurring isothiocyanates, such as benzyl isothiocyanate (BITC), are effective cancer chemopreventive compounds. To identify and characterize the potential inhibitory mechanisms of GST P1-1 induced by isothiocyanate conjugates, we studied the binding of GST P1-1 and some cysteine mutants to the BITC-SG conjugate as well as to the synthetic S-(N-benzylcarbamoylmethyl)glutathione conjugate (BC-SG). We report here the inactivation of GST P1-1 through the covalent modification of two Cys47 residues per dimer and one Cys101. The evidence has been compiled by isothermal titration calorimetry (ITC) and electrospray ionization mass spectrometry (ESI-MS). ITC experiments suggest that the BITC-SG conjugate generates adducts with Cys47 and Cys101 at physiological temperatures through a corresponding kinetic process, in which the BITC moiety is covalently bound to these enzyme cysteines through an S-thiocarbamoylation reaction. ESI-MS analysis of the BITC-SG incubated enzymes indicates that although the Cys47 in each subunit is covalently attached to the BITC ligand moiety, only one of the Cys101 residues in the dimer is so attached. A plausible mechanism is given for the emergence of inactivation through the kinetic processes with both cysteines. Likewise, our molecular docking simulations suggest that steric hindrance is the reason why only one Cys101 per dimer is covalently modified by BITC-SG. No covalent inactivation of GST P1-1 with the BC-SG inhibitor has been observed. The affinities and inhibitory potencies for both conjugates are high and very similar, but slightly lower for BC-SG. Thus, we conclude that the presence of the sulfur atom from the isothiocyanate moiety in BITC-SG is crucial for its irreversible inhibition of GST P1-1.

In vitro and in vivo antifungal activity of synthetic pure isothiocyanates against Sclerotinia sclerotiorum

BACKGROUND

Isothiocyanates (ITCs) released by the enzymatic hydrolysis of glucosinolates in the Brassicaceae are potentially useful for controlling fungal pathogens. In vitro activity of pure ITCs against Sclerotinia sclerotiorum (Lib.) de Bary was studied by adding them to glass filters in petri dishes and dissolving them in the growing media.

RESULTS

Methyl, allyl and benzyl ITCs were the most fungitoxic of the compounds in bioassays with S. sclerotiorum isolate Ss31. In the volatile phase, mycelial growth was completely inhibited by these three compounds. Aromatic ITCs were less toxic in the petri dishes but were more toxic than aliphatic ITCs when dissolved in the agar. Benzyl ITC exhibited the highest inhibitory effect on sclerotial germination, with an EC(50) value of 75.1 µmol L(-1) . Butyl and benzyl ITCs reduced apothecial production of S. sclerotiorum by 92.5% at the highest concentration. In in vivo assay, only allyl and 2-phenylethyl ITCs reduced disease incidence (by 76.7 and 70% respectively) at low concentrations.

CONCLUSION

Sclerotinia sclerotiorum in the soil might be suppressed by the higher concentrations of allyl and benzyl ITCs released from decomposition of Brassica juncea, B. carinata, B. nigra and Sinapis spp.

Synthesis and luminescent properties of the lanthanide isothiocyanate complexes with an amide-type tripodal ligand

Solid complexes of lanthanide isothiocyanates with an amide-type tripodal ligand, 2,2',2''-nitrilotris-(N-phenylmethyl)-acetamide (L) have been synthesized and characterized by elemental analysis, infrared spectra and molar conductivity measurements. At the same time, the luminescent properties of the Sm(III), Eu(III), Tb(III), Dy(III) isothiocyanate complexes in solid state and the Tb(III) complex in solvents were also investigated.

Synthesis of α- and β-Glycosyl Isothiocyanates via Oxazoline Intermediates

A practical synthesis of acylated glycosyl isothiocyanates from sugar oxazolines, by reaction with thiophosgene, is reported. In the absence of any additive, the reaction is governed by the reverse anomeric effect, leading to the equatorially oriented isothiocyanate. However, in the presence of copper(II) chloride, the reaction proceeds preferentially with retention of the configuration at the anomeric center, providing the axial anomer as the major product. Noteworthy, this strategy allows accessing per-O-acetylated glycopyranosyl isothiocyanates with 1,2-cis relative configuration (e.g., the alpha-anomer in the D-gluco and D-galacto series), a problem that was outside the scope of previous methodologies.

Isothiocyanates from tosyl chloride mediated decomposition of in situ generated dithiocarbamic acid salts

A facile and general protocol for the preparation of isothiocyanates from alkyl and aryl amines is reported. This method relies on a tosyl chloride mediated decomposition of a dithiocarbamate salt that is generated in situ by treatment of an amine with carbon disulfide and triethylamine. Utilizing this protocol, we have prepared 19-alkyl- and arylisothiocyanates in moderate to excellent yield.

Synthesis of N- and S-bis-protected lactosyl isothiobiurets

Several N,S-bis(hepta-O-acetyllactosyl)-1-aryl-2-isothiobiuret compounds have been synthesised for the first time by the reaction of S-(hepta-O-acetyl-beta-lactosyl)-1-arylisothiocarbamides and hepta-O-acetyl-beta-lactosyl isocyanate. The identities of these newly synthesised compounds were established on the basis of elemental analysis and IR, (1)H NMR, (13)C NMR and mass spectral studies.

Effect of synthetic hydroxy isothiocyanates on a bacterial virus and DNA

The Effect of hydroxy isothiocyanates on a bacterial virus and M13 DNA was examined. Hydroxy-substituted phenyl and phenyl alkyl isothiocyanates, especially 2-(3,4-dihydroxyphenyl)ethyl isothiocyanate(IT-Dop) synthesized from dopamine, showed antiviral activity on psiK. In transfection experiments with M13 mp DNA species, IT-Dop inhibited the single-stranded (SS) molecule more effectively than the double stranded replicative form (RF) DNA. These effects were dependent on reaction time, and on IT-Dop concentration. An additional experiment indicated that treatment with IT-Dop suppressed annealing (reassociation) of denatured DNA. These results indicate that IT-Dop reacts mildly with virus and SS DNA.

Efficient synthesis of isothiocyanates based on the tandem Staudinger/aza-Wittig reactions and mechanistic consideration of the tandem reactions

The tandem and stepwise Staudinger/aza-Wittig reactions of several azides were examined in detail. The tandem reaction method (Method I) exhibited superior results in the yield of the corresponding isothiocyanates bearing an electron-withdrawing group than the conventional stepwise method (Method II) which involves the sequential treatment of the azides with triphenylphosphine and then carbondisulfide. The mechanistic consideration for both reaction methods was proposed on the basis of the 1H-NMR analyses.

Validation of a Novel CHX-A‘ ‘ Derivative Suitable for Peptide Conjugation: Small Animal PET/CT Imaging Using Yttrium-86-CHX-A‘ ‘-Octreotide

A versatile bifunctional chelating reagent based on a preorganized cyclohexyl derivative of DTPA (CHX-A'') has been developed for the convenient N-terminal labeling of peptides with metal ion radionuclides of Bi(III), In(III), Lu(III), or Y(III). This was achieved via the synthesis of a mono-N-hydroxysuccinimidyl penta-tert-butyl ester derivative of CHX-A'' (trans-cyclohexyldiethylenetriaminepenta-acetic acid) featuring a glutaric acid spacer. Commercially obtained octreotide was modified at its N-terminus by this reagent in the solution phase, and its subsequent radiolabeling with (111)In (T(1/2) = 2.8 d) and (86)Y (T(1/2) = 14.7 h) demonstrated. Small animal PET/CT imaging results of (86)Y-CHX-A''-octreotide in a somatostatin receptor-positive tumor-bearing rat model are presented for the validation of the novel agent.

Preventive effect of oral administration of 6-(methylsulfinyl)hexyl isothiocyanate derived from wasabi (Wasabia japonica Matsum) against pulmonary metastasis of B16-BL6 mouse melanoma cells

AIM

Effect of oral administration of 6-(methylsulfinyl)hexyl isothiocyanate (6-MITC) or a 6-MITC-containing T-wasabi fraction from wasabi root (Wasabia japonica Matsum) to inhibit the macroscopic pulmonary metastasis was studied with a murine B16-BL6 melanoma model.

METHOD

Two administration routes, subcutaneous or intravenous, and two administration times, prior to or concomitant with tumor inoculation, of 6-MITC or T-wasabi against the metastatic foci formation in C57BL/6J mouse lungs were compared.

RESULTS

The number of metastasized foci per lung in either subcutaneous or intravenous injection was significantly reduced by intake of 6-MITC or a T-wasabi fraction. The maximum reduction by a T-wasabi fraction reached to 82%. Fifty-six percent of foci formation was inhibited by a 2 week-prior administration of 6-MITC (200 microM), whereas only 27% inhibition was obtained by a concomitant administration with tumor inoculation. Neither 6-MITC nor T-wasabi at tested concentrations showed any toxic effects.

DISCUSSION

Together with our previous results, a component of the Japanese pungent spice, wasabi appears to inhibit not only tumor cell growth but also tumor metastasis. Therefore, 6-MITC from wasabi is apparently a useful dietary candidate for controlling tumor progression.

High affinity electrophilic and photoactivatable covalent endocannabinoid probes for the CB1 receptor

We have designed and synthesized the first two high affinity covalent anandamide probes for the CB1 receptor by introducing either an electrophilic isothiocyanato or a photoactivatable azido group at the terminal carbon of the arachidonic acid moiety. The headgroup of these anandamide analogues was optimized by using a cyclopropylamide substituent to impart optimal CB1 affinity. Both 20-isothiocyanato-eicosa-5,8,11,14-tetraenoic acid cyclopropylamide (1, AM3677) and 20-azido-eicosa-5,8,11,14-tetraenoic acid cyclopropylamide (2, AM3661) exhibited high selectivities for the CB1 receptor with K(i) values of 1.3 and 0.9 nM, respectively. Using suitable experimental conditions, both ligands were shown to covalently label the CB1 receptor with high efficiency. These two covalent probes for the endocannabinoid CB1 binding site open the door for exploring the ligand binding motifs involved in the activation of the CB1 receptor by its endogenous ligand, anandamide.

Near IR emitting isothiocyanato-substituted fluorophores: their synthesis and bioconjugation to monoclonal antibodies

Two near IR emitting fluorophores, based on the phthalocyanine and naphthalocyanine chromophores, which also bear a single isothiocyanato group suitable for conjugation to proteins are reported; their utility as luminescent probes is demonstrated by conjugation to monoclonal antibodies and the ability of these conjugates to selectively bind cells bearing the relevant antigen.

A novel three-component reaction designed by the combinatorial method: Heteroarenes, isothiocyanates and isocyanides

The novel three-component reaction of isoquinoline with isothiocyanates and isocyanides leads to a variety of new imidazoisoquinolines. The zwitterionic ground state of these new ring systems is established by means of NMR and X-ray analysis. Use of phthalazine instead of isoquinoline gives access to imidazole annulated phthalazines.

Synthesis and spectroscopic characterisation of new ESIPT fluorescent protein probes

Three new benzazole isothiocyanate fluorescent dyes, 2-(4'-isothiocyanate-2'-hydroxyphenyl)benzoxazole, 2-(4'-isothiocyanate-2'-hydroxyphenyl)benzothiazole and 2-(4'-isothiocyanate-2'-hydroxyphenyl)benzimidazole were synthesised, purified until optical purity grade and characterised by spectroscopic techniques. UV/VIS and steady-state fluorescence were also applied to characterise the photophysical behaviour of the dyes. These dyes exhibit an intense fluorescence emission with a large Stokes shift, inherent to the class of benzazoles which relax by the excited state intramolecular proton transfer (ESIPT) mechanism. The dyes were studied for labeling bovine serum albumin (BSA), resulting conjugates BSA-dye with a remarkable photostability under UV/VIS radiation in relation to classical protein labels. The resulting conjugates presented fluorescence in the blue-green region. Direct fluorescence detection of protein-labeled with those dyes after polyacrylamide gel electrophoresis indicates their potential use as fluorescent probes for proteins.

Novel Azido and Isothiocyanato Analogues of [3-(4-Phenylalkylpiperazin-1-yl)propyl]bis(4-fluorophenyl)amines as Potential Irreversible Ligands for the Dopamine Transporter

Potential irreversible ligands were prepared, based on a series of 3-(1-piperazinyl)propyl-N,N-bis(4-fluorophenyl)amines, as molecular probes for the dopamine transporter (DAT). Both azido- and isothiocyanato-substituted phenylalkyl analogues were synthesized and evaluated for displacement of [(3)H]WIN 35 428 in rat caudate putamen tissue. All of the analogues showed moderate binding potencies at the DAT. The azido analogue, 16b, was radioiodinated and used to photolabel human DAT-transfected HEK 293 cell membranes. [(125)I]16b irreversibly labeled an approximately 80 kDa band corresponding to the DAT detected by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. This radioligand provides a novel addition to the growing arsenal of structurally diverse irreversible ligands that are being used to identify binding domains on the DAT. Characterizing points of attachment of these irreversible probes to the DAT protein will ultimately help elucidate the three-dimensional arrangement of the transmembrane domains, identify individual binding sites of the DAT inhibitors, and direct future drug design.

Potent isothiocyanate inhibitors of carbonic anhydrase: synthesis and evaluation

The reversible hydration of carbon dioxide by carbonic anhydrase (CA) regulates pH and carbon dioxide concentrations in diverse biological systems. Potent irreversible inhibition of CA would facilitate study of the dynamics of CA turnover as well as therapeutic effects due to long-term inhibition of the enzyme. We have synthesized isothiocyanate-containing sulfonamide inhibitors of CA from the corresponding aminosulfonamides. Significant increases in apparent binding of some of the isothiocyanate inhibitors over the amine analogues were consistent with covalent inhibition of the enzyme.

Regioselective covalent modification of hemoglobin in search of antisickling agents

Although the molecular defect in sickle hemoglobin that produces sickle cell disease has been known for decades, there is still no effective drug treatment that acts on hemoglobin itself. In this work, a series of diversely substituted isothiocyanates (R-NCS) were examined for their regioselective reaction with hemoglobin in an attempt to alter the solubility properties of sickle hemoglobin. Electrospray mass spectrometry, molecular modeling, X-ray crystallography, and conventional protein chemistry were used to study this regioselectivity and the resulting increase in solubility of the modified hemoglobin. Depending on the attached R-group, the isothiocyanates were found to react either with the Cysbeta93 or the N-terminal amine of the alpha-chain. One of the most effective compounds in the series, 2-(N,N-dimethylamino)ethyl isothiocyanate, selectively reacts with the thiol of Cysbeta93 which, in conjunction with the cationic group, was seen to perturb the local hemoglobin structure. This modified HbS shows an approximately 30% increase in solubility for the fully deoxygenated state, along with a significant increase in oxygen affinity. This compound and a related analogue appear to readily traverse the erythrocyte membrane. A discussion of the relation of these structural changes to inhibition of gelation is presented. The dual activities of increasing HbS oxygen affinity and directly inhibiting deoxy HbS polymerization, in conjunction with facile membrane traversal, suggest that these cationic isothiocyanates show substantial promise as lead compounds for development of therapeutic agents for sickle cell disease.

Rigid-core fluorescent oligothiophene-S,S-dioxide isothiocyanates. Synthesis, optical characterization, and conjugation to monoclonal antibodies

In this paper we report the synthesis of a new class of fluorescent thiophene-based isothiocyanates containing a 3,5-disubstituted dithieno[3,2-b:2',3'-d]thiophene-4,4-dioxide moiety as the rigid core, using the palladium-catalyzed cross-coupling reaction of aryl stannanes with aryl bromides (Stille coupling). By changing the molecular structure through the progressive addition of thienylene or phenylene units, light emission from blue to orange was obtained. Photoluminescence quantum yields ranged from 0.65 to 0.90 for blue and green light emitters to 0.10-0.35 for yellow and orange ones. Optically and chemically stable fluorescent bioconjugates were prepared by spontaneous reaction of the isothiocyanates with monoclonal antibodies anti-CD3 and anti-CD8 in slightly basic solutions.

One-step synthesis of non-anomeric sugar isothiocyanates from sugar azides

Tandem Staudinger-aza-Wittig reaction of primary azidodeoxy sugars with triphenylphosphine-carbon disulfide affords the corresponding primary deoxyisothiocyanato sugars in high yield. No products arising from O --> N acyl migration or formation of dimeric carbodiimides were observed. Interestingly, a polymer-supported triarylphosphine can advantageously replace triphenylphosphine, thus limiting the purification step to a simple filtration process. The reaction also allows the preparation of 5-deoxy-5-isothiocyanato sugars, a hitherto unknown class of compounds, from the corresponding azide precursors. Secondary sugar azides bearing the azido group at an endocyclic carbon atom afforded much lower isothiocyanation yields under these reaction conditions.

Oligothiophene isothiocyanates as fluorescent markers

Thiophene oligomers have been studied so far mainly for their semiconductor and charge-transport properties. However, these compounds are also highly fluorescent and soluble. Solubility and fluorescence frequencies and efficiencies can be tailored by means of appropriate functionalization of the aromatic backbone. Functionalization with the isothiocyanate group (-N=C=S) allows these molecules to form covalent bonds with NH2-containing biomolecules and give rise to optically and chemically very stable fluorescent bioconjugates. Examples of photostable conjugates formed with monoclonal antibodies are reported.

Design and evaluation of affinity labels of functionalized amino acid anticonvulsants

Studies have shown that functionalized amino acids (FAA) exhibit outstanding activity in the maximal electroshock-induced seizure (MES) test in rodents. Affinity labels patterned in part after the potent antiepileptic (R)-N-benzyl-2-acetamido-3-methoxypropionamide ((R)-2) have been prepared as mechanistic probes to learn the pharmacological basis for FAA function. The chemical reactivity of the affinity labels with nucleophiles was assessed, and the labels were evaluated in in vitro radioligand assays and in the MES tests in rodents. The affinity labels did not bind to receptors known to effect seizure spread. Three affinity labels, (R,S)-N-benzyl-2-acetamido-6-isothiocyanatohexanamide ((R,S)-5), (R)-N-(4-isothiocyanatobenzyl)-2-acetamido-3-methoxypropionamide ((R)-6), and (R)-N-(3-isothiocyanatobenzyl)-2-acetamido-3-methoxypropionamide ((R)-7), possessed excellent in vivo anticonvulsant activity and exhibited maximal activity at later time periods than typically observed for FAA. The anticonvulsant activity of 6 and 7 resided primarily in the (R)-enantiomer and the activity of (R)-6 and (R)-7 in rats (po) exceeded that of phenytoin. The chemical properties, pharmacological profile, and marked stereospecificity associated with 6 and 7 anticonvulsant activity make these compounds useful pharmacological tools for the study of the mode of action of FAA.

Novel tropane-based irreversible ligands for the dopamine transporter

3alpha-(diphenylmethoxy)tropane (benztropine) and its analogues are tropane ring-containing dopamine uptake inhibitors that display binding and behavioral profiles that are distinct from cocaine. We previously prepared a benztropine-based photoaffinity label [125I]-(N-[4-(4'-azido-3'-iodophenyl)butyl]-3alpha-[bis(4'-fluorophenyl)methoxy]tropane, [125I]1, that covalently attached to the 1-2 transmembrane spanning region of the dopamine transporter (DAT). This was in contrast to the 4-7 transmembrane spanning region labeled by a cocaine-based photoaffinity label, [125I] 2 (RTI 82). To characterize further these different binding domains, photoaffinity ligands that had the 4'-azido-3'-iodophenyl substituent extended from the same position on the tropane ring were desirable. Thus, identification of the optimal alkyl linker between this substituent and the tropane nitrogen in the benztropine series was investigated to ultimately prepare the identical N-substituted analogue of 2. In this pursuit, the N-[4-(4'-azido-3'-iodophenyl)propyl] analogue of 3alpha-[bis(4'-fluorophenyl)methoxy]tropane (9a) was synthesized as well as two isothiocyanate analogues that do not require photoactivation (10a,b) for irreversible binding. The synthesis of these target compounds was achieved using a modification of the strategy developed for 1. Evaluation of these compounds for displacing [3H]WIN 35 428 binding at DAT in rat caudate putamen revealed that the 4'-azido-3'-iodophenylbutyl substituent, found in 1, provided optimal binding affinity and was chosen to replace the N-CH3 group on 2. Both the 4'-azido-3'-iodophenyl- and the 4'-isothiocyanatophenylbutyl analogues of 2 (25 and 26, respectively) were synthesized. Both products bound to DAT with comparable potency (IC(50) = 30 nM) to RTI 82 (2). In addition, compound 26 demonstrated wash-resistant displacement of [3H]WIN 35 428 in HEK 293 cells stably transfected with hDAT. These ligands will provide important tools for further characterizing the binding domains for tropane-based dopamine uptake inhibitors at the DAT.

Lipase-catalyzed synthesis of fatty acid diethanolamides

Diethanolamides are nonionic emulsifiers widely used in industries such as cosmetics and as corrosion inhibitors. Candida antarctica lipase (Novozym 435) was used to catalyze the amidation of various fatty acids with diethanolamine. Contents of fatty acids, metal ions, and water affected the yields of diethanolamides. Hexanoic acid was the best substrate among all acyl donors. Yields of hexanoyl diethanolamide (HADEA), lauroyl diethanolamide (LADEA), and oleoyl diethanolamide (OADEA), obtained after 24 h of lipase-catalyzed reaction at 50 degrees C and 250 rpm with 90 mM fatty acid and 360 mM diethanolamine in acetonitrile, were 76.5, 49.5, and 12.1%, respectively. Addition of 1 mM metal salts increased the yields of HADEA and LADEA. Kinetic analysis showed that the yields of HADEA and LADEA in lipase-catalyzed reactions were largely associated with the rate of the forward reaction constant k(1). Anhydrous enzyme was found to be the best for the amidation reaction. Study on the enzyme operational stability showed that C. antarctica lipase retained 95 and 85% of the initial activity for the syntheses of HADEA and LADEA, respectively (even after repeated use for 10 days). The reaction runs smoothly without the use of hazardous reactants, and the developed method is useful for the industrial application.

Oligothiophene isothiocyanates as a new class of fluorescent markers for biopolymers

The regioselective synthesis of fluorescent oligothiophene isothiocyanates is described. The isothiocyanates were reacted with bovine serum albumin (BSA) following standard procedures and the optical properties of the oligothiophene-BSA conjugates were analyzed as a function of oligomer concentration, time, and irradiation power. The oligothiophene-BSA conjugates were chemically very stable and their photoluminescence characteristics persisted unaltered for several months. Photoluminescence data relative to the conjugate of an oligothiophene-S,S-dioxide isothiocyanate with monoclonal anti-CD8 antibody are reported. No fluorescence quenching was observed following the binding of the isothiocyanate to the antibody and the conjugate displayed high chemical stability and photostability.

Synthesis and evaluation of a macrocyclic bifunctional chelating agent for use with bismuth radionuclides

The detailed synthesis of the bifunctional chelating agent 2-(p-isothiocyanatobenzyl)-1,4,7,10,13-pentaazacyclopentadecane-N,N',N",N"',N""-pentaacetic acid (BF_PEPA) is reported. This ligand was conjugated to monoclonal antibody B3 and the resultant immunoconjugate radiolabeled with (205,206)Bi. The in vivo stability of the radiolabeled immunoconjugate, and targeting characteristics were determined by biodistribution studies in A431 xenograft tumor-bearing mice sacrificed at 0.5, 1, 2, 4, and 24 hr. Results indicate that BF_PEPA appears to not be a suitable bifunctional chelating agent for sequestering isotopes of Bi(III) for radioimmunotherapy applications.

Synthesis and evaluation of isothiocyanate-containing derivatives of the delta-opioid receptor antagonist Tyr-Tic-Phe-Phe (TIPP) as potential affinity labels for delta-opioid receptors

Derivatives of the delta-opioid receptor-selective peptide antagonist H-Tyr-Tic-Phe-Phe-OH (TIPP) containing an isothiocyanate moiety at the para position of either Phe(3) or Phe(4) were prepared as potential affinity labels for delta-opioid receptors. The synthesis was accomplished using a general solution-phase synthetic procedure which allows for introduction of affinity labeling groups late in the synthesis of a variety of small peptide substrates. The target peptides and their corresponding amines were then evaluated in radioligand binding experiments using Chinese hamster ovary (CHO) cells expressing delta- and mu-opioid receptors. The peptides [Phe(p-NCS)(3)]TIPP (2) and [Phe(p-NCS)(4)]TIPP (4) showed affinity for delta-receptors comparable to the parent compound TIPP (IC(50) = 12 and 5 nM, respectively, vs 6 nM for TIPP). Both peptides 2 and 4 were able to inhibit radioligand binding to delta-receptors in a wash-resistant manner at a concentration of 10 nM. Therefore, the peptides [Phe(p-NCS)(3)]TIPP (2) and [Phe(p-NCS)(4)]TIPP (4) represent two affinity labels that may prove useful in the study of delta-opioid receptors.

A mass spectrometry screening method for antiaggregatory activity of proteins covalently modified by combinatorial library members: application to sickle hemoglobin

A homogeneous assay, based on electrospray mass spectrometry, is described for identifying compounds in a combinatorial library that covalently modify a protein and thereby enhance its solubility. The technique is based on measuring the distribution of modified proteins in the supernatant versus aggregate. Compounds having the greatest anti-aggregatory activity are those with the highest supernatant/aggregate ratio. Mass is used as a marker to identify which covalent modifier in the library is involved. An exploratory study is presented which demonstrates that the antisickling activity of a family of isothiocyanates, as measured by the standard C(sat) assay, correlates well (r(2) = 0.98) with the mass spectrometry analysis of the supernatant/aggregate distribution. The technique has potential for screening libraries capable of covalently modifying other proteins of clinical interest, e.g., Alzheimer's, Huntington's, and various prion related diseases.

Chiral nonsteroidal affinity ligands for the androgen receptor. 1. Bicalutamide analogues bearing electrophilic groups in the B aromatic ring

A series of chiral analogues of bicalutamide bearing electrophilic groups (isothiocyanate, N-chloroacetyl, and N-bromoacetyl) on aromatic ring B of the parent molecule were synthesized. These compounds were designed as affinity ligands for the androgen receptor (AR). We prepared the (R)- and (S)-optical isomers of these compounds as pure enantiomers. The AR binding affinities of these compounds were measured in a competitive binding assay with the radiolabeled high-affinity AR ligand, [(3)H]mibolerone. In accordance with our previous results for the enantiomers of bicalutamide, we found that all (R)-isomers demonstrated much higher binding affinity to the AR as compared to their corresponding (S)-isomers. The para-substituted affinity ligands in ring B bound the AR with higher affinities than the corresponding meta-substituted analogues. Oxidation of thioester affinity ligands to their sulfonyl analogues for the para-substituted compounds decreased AR binding affinities and similar modification increased binding affinities for corresponding meta-analogues. The least potent para-substituted sulfonyl compounds had higher AR binding affinities than the most potent meta-substituted sulfonyl compounds. Overall, the para-substituted unoxidized molecules demonstrated the highest AR binding affinity. Subsequent research using AR exchange assays and Scatchard analyses showed that the isothiocyanate affinity ligands (R)-7, (R)-9, and (R)-10 reported herein are the first specific chemoaffinity ligands for the AR.

Development of an amino acid sequence and D/L-configuration determination method of peptide with a new fluorescence Edman reagent, 7-methylthio-4-(2,1,3-benzoxadiazolyl) isothiocyanate

On the basis of the relationship between the fluorescence characteristics of the benzofurazan compounds and the Hammett constants (sigma p), a new fluorescence Edman reagent, 7-methylthio-4-(2,1,3-benzoxadiazolyl) isothiocyanate (MTBD-NCS) was designed and synthesized. MTBD-thiohydantoin (TH)-amino acid derivatives produced by the Edman sequencing method gave fluorescence, whereas other degradation byproducts such as MTBD-thiocarbamoyl (TC)- or carbamoyl (CA)-amino acids did not fluoresce. MTBD-NCS was applicable as an Edman sequencing reagent to the simultaneous determination of both the sequence and D/L-configuration of amino acids in peptides. Boron trifluoride (BF3) and HC1/methanol were adopted as the cyclization/cleavage and conversion reagents to suppress the amino acid residue racemization. The MTBD-TH-amino acids were separated on a reversed-phase column for amino acid sequencing, and their enantiomers were resolved on two types of polysaccharide-based chiral stationary phases for D/L-configuration determination. The method was successfully applied to the sequence and D/L-configuration determination of D-amino acid-containing peptide [D-Ala2]-deltorphin II.

Synthesis of 6,7-dideoxy-7-isothiocyanatoheptoses: stable fully unprotected monosaccharide isothiocyanates

Methyl 6,7-dideoxy-7-isothiocyanato-alpha-D-gluco (manno)(galacto)-heptopyranosides have been synthesized in four steps by homologation of the respective methyl hexopyranosides via the corresponding heptopyranosydurononitriles. Neither intra- nor intermolecular thiocarbamate formation was observed, even under rather strenuous acidic or basic conditions. The reducing derivative 6,7-dideoxy-7-isothiocyanato-alpha-D-gluco-heptopyranose was also a stable compound in aqueous solution in the absence of base. Formation of a six-membered intramolecular cyclic thiocarbamate was achieved in DMF solution in the presence of triethylamine. The title compounds are the first examples of stable fully unprotected monosaccharide isothiocyanates.

Synthesis, characterization, and evaluation of a novel bifunctional chelating agent for the lead isotopes 203Pb and 212Pb

Radioisotopes of Pb(II) have been of some interest in radioimmunotherapy and radioimmunoimaging (RII). However, the absence of a kinetically stable bifunctional chelating agent for Pb(II) has hampered its use for these applications. 203Pb (T(1/2) = 52.02 h) has application potential in RII, with a gamma-emission that is ideal for single photon emission computerized tomography, whereas 212Pb (T(1/2) = 10 h) is a source of highly cytotoxic alpha-particles via its decay to its 212Bi (T(1/2) = 60 min) daughter. The synthesis of the novel bifunctional chelating agent 2-(4-isothiocyanotobenzyl)-1,4,7,10-tetraaza-1,4,7,10-tetra- (2-carbamoyl methyl)-cyclododecane (4-NCS-Bz-TCMC) is reported herein. The Pb[TCMC]2+ complex was less labile to metal ion release than Pb[DOTA]2- at pH 3.5 and below in isotopic exchange experiments. In addition to increased stability to Pb2+ ion release at low pH, the bifunctional TCMC ligand was found to have many other advantages over the bifunctional 1,4,7,10-tetraazacyclodocane-1,4,7,10-tetraacetic acid (DOTA) ligand. These include a shorter and more straightforward synthetic route, a more efficient conjugation reaction to a monoclonal antibody (mAb), with a higher chelate to protein ratio, a higher percent immuroreactivity, and a more efficient radiolabeling reaction of the mAb-ligand conjugate with 203Pb.

Comparison of 225actinium chelates: tissue distribution and radiotoxicity

The biodistribution and tissue toxicity of intravenously administered 225-actinium (225Ac) complexed with acetate, ethylene diamine tetraacetic acid (EDTA), 1, 4, 7, 10, 13-pentaazacyclopentadecane-N, N', N", N"', N""-pentaacetic acid (PEPA), or the "a" isomer of cyclohexyl diethylenetriamine pentaacetic acid (CHX-DTPA), were examined. The percent of injected dose per organ and per gram of tissue for each chelate complex was determined. 225Ac-CHX-DTPA was evaluated further for radiotoxic effects. Mice receiving > or =185 kBq 225Ac-CHX-DTPA suffered 100% morbidity by 5 days and 100% mortality by 8 days postinjection, and all animals evaluated had significant organ damage. The in vivo instability of the 225Ac-CHX-DTPA complex likely allowed accumulation of free 225Ac in organs, which resulted in tissue pathology.

Thiol-containing RNA for the study of structure and function of ribozymes

RNA performs multiple functions in cellular environments, such as transferring genetic information, catalyzing chemical reactions, and providing an integral component of ribonucleoprotein complexes involved in mRNA processing and translation. Many of these functions are poorly understood, mainly due to the lack of structural information. Because limited information has been obtained by physical and biophysical techniques, chemical and biochemical methods have been extensively used for studying RNA structure. This article outlines one such method which relies on site-specific incorporation of thiols into RNA. A brief overview of the methods for incorporation of thiols into RNA is followed by a detailed description of a procedure which utilizes postsynthetic modification of 2'-amino-containing RNA for incorporation of thiols. The use of thiol-containing RNA to form disulfide cross-links for the study of the structure and dynamics of ribozymes is subsequently described.

Isoxazolylthioamides as potential immunosuppressants a combinatorial chemistry approach

A library of thioamide derivatives of leflunomide 1a and of its bioactive metabolite 1b has been synthesised on solid phase. Thus, para-substituted phenylacetic acids were coupled to TentaGel and were subsequently reacted with aromatic isothiocyanates. Treatment of the resulting enaminothioamides with hydroxylamine led to their simultaneous cyclisation and cleavage from the resin affording 2-25. Their in vitro profiling demonstrated that the amide-thioamide isologous substitution was detrimental of the biological activity.

Isothiocyanate derivatives of 9-[3-(cis-3,5-dimethyl-1-piperazinyl)propyl]carbazole (rimcazole): irreversible ligands for the dopamine transporter

Cocaine has been reported to bind to the dopamine transporter in a biphasic fashion, and it has been hypothesized that the low-affinity component may play a modulatory role in cocaine's psychomotor stimulant effects. In an effort to gain further insight into the roles of the two sites, we have prepared a series of irreversible ligands based on rimcazole (9-[3-(cis-3,5-dimethyl-1-piperazinyl)propyl]carbazole, 2), a compound that has been postulated to bind only to the low-affinity site. The alkylating moiety (isothiocyanate) is attached to the distal nitrogen of the piperazine ring via alkyl chains of varying lengths or directly attached to one of the aromatic groups. It was found that substitution on the piperazine nitrogen caused an initial decrease in affinity that was recovered as the alkyl chain length increased. Importantly, the analogue 16, with the highest affinity for the dopamine transporter (DAT), binds in a monophasic and irreversible manner, as evidenced by the greatly diminished binding of [3H]WIN 35,428 in tissue that had been preincubated with the ligand and then thoroughly washed using centrifugation. The dose-dependent reduction in Bmax was accompanied by a concentration-related decrease in KD values. This shift in KD to a lower value suggests that the preincubation with 16 produced a preferential irreversible binding to the low-affinity [3H]WIN 35,428 site on the dopamine transporter. These ligands may prove to be important tools with which to study the significance of the low-affinity site on the DAT. Since rimcazole does not share the behavioral profile of cocaine, and in fact appears to play a modulatory role, these compounds may provide leads for a novel cocaine-abuse treatment.

Stereochemical influence on the stability of radio-metal complexes in vivo. Synthesis and evaluation of the four stereoisomers of 2-(p-nitrobenzyl)-trans-CyDTPA

Distinct differences in in vivo stability of the two diastereomeric C-Functionalized CyDTPA chelating agents, (CHX-A DTPA and CHX-B DTPA, both racemates), as recently reported prompted further investigation as to why differences in configuration produced striking effects on the in vivo stability of their yttrium complexes. To this end, the four individual component stereoisomers of CHX-A and CHX-B were synthesized and ability to bind yttrium was investigated both in vitro and in vivo.

Chemical carboxy-terminal sequence analysis of peptides using acetyl isothiocyanate

A new derivatizing reagent, acetyl isothiocyanate (AITC), is applied for C-terminal peptide sequencing. It has been successfully used to sequence six C-terminal residues of a synthetic peptide at low nanomole levels. According to the mechanism study of the derivatization of C-terminal amino acid with various reagents, the derivatizing reagents (R-N=C=S or SCN-) were classified into three types: type I, the ionic compound (e.g., HSCN, NH4SCN, KSCN); type II, R is a good leaving group (e.g., TMS-ITC, TBSn-ITC); type III, R is reactive (e.g., AITC, BITC, DPP-ITC). Type III reagents are superior to other reagents because their double-function of activation and derivatization. Unlike type I and type II reagents, type III reagent chemistry does not require oxazolinone formation which can cause racemization. Compared with benzoyl isothiocyanate, diphenyl phosphoroisothiocyanatidate, trimethylsilyl isothiocyanate, and ammonium thiocyanate, AITC is the most effective derivatizing reagent. As a type III reagent, AITC possesses some features such as no need for oxazolinone formation, no requirement for separate activation step, high reactivity, easy preparation, and low absorption at 260-270 nm. Different reaction conditions were investigated for optimization and the chemical mechanism of AITC chemistry is illustrated. A convenient and efficient approach for synthesis of amino acid thiohydantoins as reference standards has also been developed.