Heteroaromatic Frameworks Research Articles

Room temperature synthesis of triazine covalent organic frameworks for size-selective intercalation of molecules and fast water purification

In this work, we report on a new method for the construction of triazine covalent organic frameworks on gram scale by catalyst-free cyclotrimerization of alkynes at room temperature for the size-selective intercalation of molecules and fast water purification. Reaction between sodium acetylide and cyanuric chloride resulted in 2,4,6-triethynyl-1,3,5-triazine intermediate which converted to heteroaromatic frameworks comprising triazine and benzene rings upon in situ [2 + 2+2] cyclotrimerization. Mechanistic studies revealed a crucial role for the triazine ring in susceptibility of ethynyl groups to cyclization. The permeability of these nanostructures to small molecules, exemplified by Rhodamine 6G (R6G) and HAuCl4, and their impermeability to bigger objects such gold nanoparticles (5 nm) indicated their potential to remove molecular impurities from water. Impurities including Methylene blue and Malachite green with 20 mg L−1 concentration were completely removed by 1 mg of the synthesized frameworks in 60 s. Taking advantages of the straightforward synthesis and permeability to small molecules, the synthesized triazine frameworks can be used for the fast and efficient purification of water contaminated by toxic agents.

Benzothiazole alkaloids: Biomimetic synthesis of the violatinctamine scaffold and the insect-derived monoamine polyrhadopamine D

The unique heteroaromatic framework of the marine alkaloid violatinctamine has been assembled using a one-pot Pictet-Spengler-autoxidation sequence. Control studies infer the initially formed tetrahydroisoquinoline undergoes a triplet oxygen-mediated autoxidation to the dihydroisoquinoline. Further studies led to a biomimetic synthesis and structural affirmation of the insect derived monoamine polyrhadopamine D.

Synthesis of Alocasin A.

Herein is reported a synthesis of alocasin A (1), an alkaloid component of Alocasia macrorrhiza, a herbaceous plant used in folk medicine throughout southern Asia. A double Suzuki-Miyaura cross-coupling reaction between a 3-borylindole and 2,5-dibromopyrazine was used to assemble the heteroaromatic framework of the natural product. Removal of the protecting groups gave a synthetic sample of 1, the spectroscopic data of which matched those in the isolation report of this compound.

Synthesis of scalaridine A

A synthesis of the pyridine-linked bisindole alkaloid scalaridine A is described. An iridium catalyzed, directed C–H borylation of N-Boc-5-methoxyindole gave the corresponding 3-borylindole, which underwent a one-pot, double Suzuki–Miyaura cross-coupling reaction with 3,5-dibromopyridine to install the entire heteroaromatic framework of the natural product. Removal of the protecting groups gave a synthetic sample of scalaridine A, which was spectroscopically identical to that described in the isolation report.

New metal organic framework structures based on 2,5-pyridinedicarboxylate ligands and Zn2+ ions

Structural characteristics and adsorption properties of new heteroaromatic framework structures based on Zn2+ ions and 2,5-pyridinedicarboxylate ligands are investigated. A comparative study of the aromatic framework structure MOF-5 based on Zn4O clusters and 1,4-benzenedicarboxylate ligands is also performed in order to reveal the effect of the nature of the organic fragment.

Pd0-Mediated Rapid Coupling between Methyl Iodide and Heteroarylstannanes: An Efficient and General Method for the Incorporation of a Positron-Emitting11C Radionuclide into Heteroaromatic Frameworks

The Pd(0)-mediated rapid trapping of methyl iodide with an excess amount of a heteroaryl-substituted tributylstannane has been investigated with the aim of incorporating a short-lived (11)C-labelled methyl group into the heteroaromatic carbon frameworks of important organic compounds, such as drugs with various heteroaromatic structures, in order to execute a positron emission tomography (PET) study of vital systems. The reaction was first performed by using our previously developed CH(3)I/stannane/[Pd(2)(dba)(3)]/P(o-CH(3)C(6)H(4))(3)/CuCl/K(2)CO(3) (1:40:0.5:2:2:2) system in DMF at 60 degrees C for 5 min (conditions A), however, the reaction gave low yields for various heteroaromatic compounds. Increasing the amount of phosphine ligand (conditions B) led to a significant improvement in the yield, but the conditions were still not suitable for a range of basic heteroaromatic structures. Use of the CuBr/CsF system (conditions C) also provided a result similar to that obtained under conditions B with an increased amount of the phosphine. Thus, pyridine and related heteroaromatic compounds remained less reactive substrates. The problem was overcome by replacing the DMF solvent with N-methyl-2-pyrolidinone (NMP). The reaction in NMP at 60-100 degrees C for 5 min using a CH(3)I/stannane/[Pd(2)(dba)(3)]/P(o-CH(3)C(6)H(4))(3)/CuBr/CsF (1:40:0.5:16:2:5) combination (conditions D) gave the methylated products in yields of more than 80 % (based on the reaction of CH(3)I) for all of the heteroaromatic compounds listed in this study. Thus, the combined use of NMP and an increased amount of phosphine is important for promoting the reaction efficiently. The use of this general approach to rapid methylation has been well demonstrated by the synthesis of the PET tracers 2- and 3-[(11)C]methylpyridines by using [Pd(2)(dba)(3)]/P(o-CH(3)C(6)H(4))(3)/CuBr/CsF (1:16:2:5) in NMP at 60 degrees C for 5 min, which gives the desired products in HPLC analytical yields of 88 and 91 %, respectively.

Domino Carbocationic Cyclization of Functionalized Cyclopropyl Ketones: Facile One‐Pot Access to Peri‐ and Angularly Fused Polycyclic Aromatic and Heteroaromatic Frameworks.

Conjugate adducts obtained by base-induced 1,4-addition-elimination of various aryl/heteroaryl acetonitriles with 1-(2-arylcyclopropyl)-3,3-(bismethylthio)-2-propen-1-ones have been shown to undergo facile acid-induced domino carbocationic rearrangement yielding a variety of substituted tricyclic aromatic and heteroaromatic frameworks in high yields in a one-pot operation. The methodology provides efficient, high-yield routes for synthesis of novel substituted dihydrophenalenes, dihydrobenzo[d,e]anthracene, cyclopenta[a]naphthalene, and fused heteroaromatics such as substituted 4,5-dihydrobenzo[c,d]indole, dihydronaphtho[1,8-b,c]thiophene, dihydroindeno[5,4-b]- and -[4,5-b]-thiophenes, cyclopenta[a]carbazole, and dihydrocyclopenta[e]indazol-3-one derivatives. The probable mechanism of this interesting domino process appears to involve stepwise or concomitant acid-induced ring opening and intramolecular cyclocondensation of cyclopropyl ketones to give benzo-fused arene (or heteroarene) intermediates bearing a reactive benzylic carbocation that is captured intramolecularly either by a preexisting aromatic (or heteroaromatic) ring or by a newly formed benzene ring to give either peri-fused or angularly fused products, respectively. Thus, the overall domino process entails formation of two C-C bonds, a substituted benzene ring along with a peri-fused cyclohexane or angularly fused cyclopentane ring in a single operation.

Domino carbocationic cyclization of functionalized cyclopropyl ketones: facile one-pot access to peri- and angularly fused polycyclic aromatic and heteroaromatic frameworks.

Conjugate adducts obtained by base-induced 1,4-addition-elimination of various aryl/heteroaryl acetonitriles with 1-(2-arylcyclopropyl)-3,3-(bismethylthio)-2-propen-1-ones have been shown to undergo facile acid-induced domino carbocationic rearrangement yielding a variety of substituted tricyclic aromatic and heteroaromatic frameworks in high yields in a one-pot operation. The methodology provides efficient, high-yield routes for synthesis of novel substituted dihydrophenalenes, dihydrobenzo[d,e]anthracene, cyclopenta[a]naphthalene, and fused heteroaromatics such as substituted 4,5-dihydrobenzo[c,d]indole, dihydronaphtho[1,8-b,c]thiophene, dihydroindeno[5,4-b]- and -[4,5-b]-thiophenes, cyclopenta[a]carbazole, and dihydrocyclopenta[e]indazol-3-one derivatives. The probable mechanism of this interesting domino process appears to involve stepwise or concomitant acid-induced ring opening and intramolecular cyclocondensation of cyclopropyl ketones to give benzo-fused arene (or heteroarene) intermediates bearing a reactive benzylic carbocation that is captured intramolecularly either by a preexisting aromatic (or heteroaromatic) ring or by a newly formed benzene ring to give either peri-fused or angularly fused products, respectively. Thus, the overall domino process entails formation of two C-C bonds, a substituted benzene ring along with a peri-fused cyclohexane or angularly fused cyclopentane ring in a single operation.

Synthesis and antitumor evaluation of new thiazolo[5,4-b]quinoline derivatives.

A new synthesis of 9-hydroxy- and 9-(alkylamino)thiazolo[5,4-b]quinolines by cyclization of 4-(ethoxycarbonyl)-5-(arylamino)thiazoles and 5-(arylamino)-4-carbamoylthiazoles, respectively, is described. In vitro cytotoxicity of a large number of derivatives of these compounds has been tested against several cell lines. The highest activities observed are associated with the presence of a 2-[[(N,N-diethylamino)ethyl]amino] substituent at C-2 and a fluorine atom at the C-7 position of the tricyclic planar heteroaromatic framework. Three structural features seem to be essential for antitumor activities: a positive charge density at carbon C-7, a side chain at position C-2 or C-9 of the thiazoloquinoline skeleton with two basic nitrogens and a pKa value of 7.5-10 in the most basic center, and a conformational flexibility of this basic side chain. These structural requirements must be simultaneously satisfied in order to ensure a significant antitumor activity.

Non-peptide cholecystokinin-B/gastrin receptor antagonists based on bicyclic, heteroaromatic skeletons.

A series of potent and selective cholecystokinin-B/gastrin receptor antagonists based on the dibenzobicyclo[2.2.2]octane (BCO) skeleton which have recently been described were found to show species-dependent behavior when examined in rat and dog models. We now report the discovery of compounds in which the BCO skeleton has been replaced with bicyclic, heteroaromatic frameworks, such as a 5,6-disubstituted indole or benzimidazole. These new ligands maintain the affinity and selectivity profile of the previous compounds in vitro but show a much more consistent behavior pattern in vivo. Representative examples of this class of compound have been shown to inhibit pentagastrin-stimulated acid secretion when administered intravenously at doses of 0.1 mumol kg-1 or less.

Relaxation Processes in Aromatic Methyl Groups. II. Methyl-Methyl Nuclear Overhauser Enhancements

A range of compounds with methyl groups disposed ortho and peri on heteroaromatic frameworks have been prepared, and T1 values and methyl-methyl Overhauser effects measured for them. Most of the n.O.e . Values were ≤6%, but two examples of methyls flanked by two others exhibited values of 9% (6-hydroxy-4,4,5,7-tetramethyl-3,4-dihydro-2H-benzopyran-2-one) and 15% (1,4,5,8,9-pentamethylcarbazole).