1,720,972 research outputs found
1,2,4-triazoles. Improved synthesis of 5-substituited 4-amino-3mercato-(4H)-1,2,4 triazoles and a facile route to 3,6-disubstituited 1,24-triazolo[3,4b][1,3,4]thiadiazoles
No full textThe reaction of thiocarbohydrazide with carboxylic acids at the melting temperature allows an improved preparation of the 5-substituted 4-amino-3-mercapto-1,2,4-triazole heterocycles. The crude 4-amino-5-mercapto-1,2,4-triazoles react easily with carboxylic acids or carboxylic acid chlorides to afford the 1,2,4-triazolo[3,4-b][1,3,4]thiadiazole ring system
Two-carbon bridge substituted cocaines: Enantioselective synthesis, attribution of the absolute configuration and biological activity of novel 6- and 7-methoxylated cocaines
No full textIn an effort to learn more about the general structure–activity relationships of cocaine with the aim to elucidate those structural features that might confer antagonistic properties to such analogues, we describe herein our synthetic efforts to prepare two-carbon bridge functionalized (methoxylated and hydroxylated) analogues. Our approach makes use of a modification of the classical Willstatter synthesis of cocaine: Mannich type cyclization of acetonedicarboxylic acid monomethyl ester with methylamine hydrochloride and 2-methoxysuccindialdehyde in a citrate buffer solution afforded the 6- and 7-substituted 2-carbomethoxy-3-tropinones 3a,b and 4a,b in approximate yields of 64%. Reduction of the (±)-tropinone derivatives was performed with sodium amalgam in a sulfuric acid solution to afford a mixture of (±)-methoxyecgonine and (±)-methoxypseudoecgonine derivatives 5, 11 and 6, 7, 12, 13. Benzoylation of these alcohols yielded the desired cocaine and pseudococaine-like compounds 8, 14 and 9, 10, 15, 16. Additionally, we show that enzymatic hydrolysis of these cocaine analogues using pig liver esterase (PLE) affords a practical means for achieving their chemical resolution. The enantiomers of the methoxycocaine analogues were also prepared starting from chiral (+)- and (-)-6-methoxytropinone. All new analogues were examined for their ability to displace [3H]mazindol binding and to inhibit high-affinity uptake of [3H]dopamine into striatal nerve ending (synaptosomes). It appeared evident that methoxylation of the cocaine two-carbon bridge provides compounds of particular interest: the Ki for the binding of the methoxypseudococaines is about two to four times smaller than the Ki for inhibition of dopamine uptake, thus enabling these compounds capable of countering the effects of cocaine to some extent
Tetramethylguanidine (TMG)-catalyzed addition of dialkyl phosphites to alpha,beta-unsaturated carbonyl compounds, alkenenitriles, aldehydes, ketones and imines
No full textTetramethylguanidine-catalyzed addition of dialkyl phosphites to a,b-unsaturated carbonyl compounds, alkenenitriles, aldehydes and ketones constitutes a practical route to a variety of phosphonate synthons. The very mild conditions employed, together with the short reaction times, make the procedure highly versatile and tolerant to a range of functionalities. The proposed methodology is also convenient for the preparation of a-aminophosphonates
Synthesis of new 2,2 '-disubstituted 5,5 '-dimethyl-4,4 '-bitriazoles and 2-(4-triazolyl)quinoxalines
No full textThermal rearrangement of 3-acylisoxazole arylhydrazones allowed facile preparation of 2H- 1,2,3-triazoles which were firstly reacted with isoamyl nitrite and then with an opportune arylhydrazine to produce the corresponding a-hydroxyiminohydrazones 8a-h. The reaction of compounds 8a-h with phosphorus pentachloride afforded the desired 4,4'-bitriazoles 1a-h. The a-hydroxyiminoketone derivative 7 or the a-diketone 14 reacted easily with 1,2- phenylenediamine to afford 1,2,3-triazoles 2a-c bearing the quinoxaline moiety at position 4. Improved yields of the quinoxalines 2a-c were obtained when 1,2-phenylenediamine was reacted with the dioxime 15
Facile synthesis of 2-nitroalkanols by Tetramethylguanidine (TMG)-catalyzed addition of primary nitroalkanes to aldehydes and alicyclic ketones
No full textTetramethylguanidine-catalyzed addition of primary nitroalkanes to aldehydes and alicylic ketones constitutes a practical means to perform the nitro-aldol reaction (Henry reaction). The very mild conditions employed, together with the short reaction times, make the procedure tolerant of a range of functionalities and highly versatile for the synthesis of a variety of 2-nitroalkenols
Facile synthesis of pyrazoles and pyrroles via thermolysis of tetrazolo[1,5-b]pyridazines, tetrazolo[1,5-a]pyrimidines and tetrazolo[1,5-a]pyridines
No full textA simple and high yielding preparation of pyrazoles and pyrroles is described. Thermolysis of tetrazolo[1,5-b]pyridazines, tetrazolo[1,5-a]pyrimidines and tetrazolo[1,5-a]pyridines allowed easy ring contraction thus providing a facile preparation of cyanopyrazole and cyanopyrrole heterocycles. Since the cyano group is a versatile precursor of other functionalities, the reaction appears of particular interest for the construction of a variety of pyrazoles and pyrroles. The simple preparation of the starting tetrazole derivatives, the relatively mild conditions employed, and the very short reaction times make this versatile procedure of great synthetic utility and applicable both to small and large scale preparation
The synergistic apoptotic effects of thiophenfurin, an inosine monophosphate dehydrogenase inhibitor, in combination with retinoids in HL60 cells
No full textNew effective cytotoxic agents and combinations are urgently needed in cancer treatment. The enzyme inosine monophosphate dehydrogenase is a potentially useful target for drug development, since its activity has been shown to be amplified in malignant cells. Thiophenfurin, an inhibitor of the enzyme synthesized by us, is endowed with a significant apoptotic activity in promyelocytic leukaemia HL60 cells. Since retinoids were successfully employed in the treatment of patients with leukaemia, demonstrating significant differentiation-inducing and apoptotic effects, we carried out this study to evaluate the effects of the combination of thiophenfurin and several retinoid molecules, acting in different phases of the cell cycle in vitro. The results show that thiophenfurin is capable of eliciting significant S phase-specific antiproliferative effects in different sensitive and resistant cell lines with the IC50s ranging from 6.7 to 26 μM. When HL60 cells were treated with thiophenfurin in combination with retinoids, the effects on cell growth were additive or synergistic, depending on the kind of retinoid used and the sequence of treatment: In particular, we observed additive effects when the cells were exposed to thiophenfurin and all -transretinoic acid either simultaneously or sequentially. Instead, when the new heterocyclic retinoid isoxazole benzoic acid was used, synergism was obtained in the cells treated sequentially. The combination of thiophenfurin and isoxazole benzoic acid determined synergistic apoptotic effects through a mitochondrion-dependent mechanism, suggesting the possible usefulness of this combination in the treatment of leukaemia
Strong Bicyclic Guanidine Base-promoted Wittig and Horner-Wadsworth-Emmons Reactions
No full textA convenient procedure to effect the Wittig and Horner-Wadsworth-Emmons reactions employs guanidine TBD and MTBD as base-promoters;
mild reaction conditions, high efficiency, and facile isolation of the final products make the present methodology, at least in some cases, a
practical alternative to known procedures
1,5,7-Triazabicyclo[4.4.0]dec-1-ene (TBD), 7-methyl-TBD (MTBD) and the polymer-supported TBD (P-TBD): three efficient catalysts for the nitroaldol (Henry) reaction and for the addition of dialkyl phosphites to unsaturated systems
No full textThe 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) and its 7-methyl derivative (MTBD) have been proven to be of great synthetic utility as catalysts in the nitroaldol (Henry) reaction and for the addition of dialkyl phosphites to a variety of carbonyl compounds. The catalysts were in many cases superior to the parent tetramethylguanidine (TMG). In general the reaction proceeds in a few minutes at 0°C. The polymer-supported-TBD (P-TBD) was also proven to be an efficient promoter of the above cited nucleophilic additions
Structure-activity relationship studies of novel heteroretinoids: Induction of apoptosis in the HL-60 cell line by a novel isoxazole-containing heteroretinoid
No full textIn a search for retinoic acid receptor (RAR and RXR)-selective ligands, a series of isoxazole retinoids was synthesized and evaluated in vitro in transcriptional activation and competition binding assays for RARs and RXRs. In addition, these compounds were evaluated for their differentiating, cytotoxic, and apoptotic activities. In general, these derivatives showed scarcely any binding affinity and were not active in the transcriptional assay. However, among these isoxazole derivatives, the cis-isomer 14b was identified as a potent inducer of apoptosis, and its activity was found to be 6.5 and 4 times superior than that of 13-cis- and 9-cis-retinoic acids, respectively. On the other hand, compound 13b, which has the trans stereochemistry at the double bond, was found not to be active in the apoptotic assay, but it was endowed with appreciable differentiating activity. Therefore, it seems that the different stereochemistry of the double bond may be associated with a different biological activity: potent apoptotic activity for the cis-isomer but differentiating activity for the trans structure. This biological behavior was found, at least in part, for the 9-cis- and 13-cis-retinoic acids with respect to the all-transretinoic acid. Thus, structure 14b could offer an interesting model for the design of new compounds endowed with apoptotic activity
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