Synthesis of functionalized guanidino amino acids

We report the synthesis of guanidino amino acids (GuAA), which are structurally related to Arg and resemble a dipeptide consisting of alpha- and gamma-amino acid with a guanidinium group in the main chain. The compounds are available with different protecting groups in gram amounts and are intended as synthetic building blocks for the construction of synthetic oxoanion or peptide receptors. Tyr, Trp or dansyl-functionalized Lys can be introduced as the alpha-amino acid part, which leads to luminescent GuAAs. The compounds signal carboxylate binding in MeOH, DMSO and buffered water by change of the emission intensity. The property may find use in the construction of chemosensors.     

Synthesis of novel chiral amino acids possessing a porphyrin moiety

Phenylalanine derivatives bearing a porphyrin moiety at the para-position were prepared in an enantiomerically pure form. The synthetic nonnatural aromatic amino acid reacted with amines and acids to give novel functionalized peptides without loss of the enantiomeric purity.     

Synthesis of orthogonally protected cyclic homooligomers from sugar amino acids

Two new families of orthogonally protected cyclic homooligomers with two to four sugar units were synthesized from pyranoid sugar amino acids. Cyclic oligomers composed of amide-linked sugar amino acids (1-3) were prepared by cyclization of linear oligomers of the novel orthogonally protected pyranoid sugar amino acid 12 using a solution-phase coupling method. These orthogonally protected cyclic molecules can be selectively or fully deprotected, affording the macrocycles ready to further functionalization. The straightforward reduction of the amide bonds in the cyclic oligomers 1-3 gave the corresponding amine-linked macrocycles 4-6. This kind of amine-linked carbohydrate-based cyclic oligomer has never been reported before. These flexible molecular receptors could be studied as molecular hosts for molecular, cationic, and anionic recognition. Conformational analysis by molecular modeling (AM1) showed that all of the deprotected cyclic trimers and tetramers preferred a (4)C(1) chair conformation with oxygen atoms of the sugar ring located on the interior of the cavity and the secondary hydroxyl groups outward. In the amide-linked macrocycles, all of the amide bonds are in s-trans conformation. The estimated size of the internal cavity is about 4.5 A for the cyclic trimer and 6.9 A for the cyclic tetramer. The amine-linked macrocycles displayed similar conformational behavior with a slight decrease in internal cavity.     

Pd-catalyzed carbonylative reactions of aryl iodides and alkynyl carboxylic acids via decarboxylative couplings

Alkynyl carboxylic acids reacted with aryl iodides under a CO atmosphere in the presence of a palladium catalyst to produce α,β-alkynyl aryl ketones in good yields. The maximum turnover number was 16?800. The desired carbonylative coupling was formed from phenyl propiolic acid without any formation of a noncarbonylative coupling product in the absence of CuI. However, the reaction with alkyl-substituted alkynyl carboxylic acids required CuI as a cocatalyst for high yield.     

Pd-catalyzed copper-free carbonylative Sonogashira reaction of aryl iodides with alkynes for the synthesis of alkynyl ketones and flavones by using water as a solvent

The Pd-catalyzed copper-free carbonylative Sonogashira coupling reaction to synthesize alkynyl ketones from terminal alkynes and aryl iodides was achieved by using water as a solvent. The reaction was carried out at room temperature under balloon pressure of CO with Et(3)N as a base. The developed method was successfully applied to the synthesis of flavones.     

Synthesis of E-vinyl iodides via Pd-catalyzed hydrostannation of terminal alkynes

E-Vinyl iodides may be prepared via a one-pot reaction involving Pd-catalyzed hydrostannation of terminal alkynes followed by iodinolysis of the intermediate vinylstannane. The synthesis is tolerant of functional groups, such as alcohols and esters.     

Synthesis of protected pseudopeptides from dicarboxylic amino acids by Mitsunobu condensation

Four protected pseudopeptides from Glu-, Asp- and Gly-derivatives have been prepared via Mitsunobu condensation. It was shown to be a universal and preparative method which allows the formation of different structural molecules containing reduced peptides.     

Tetraalkylammonium amino acids as functionalized ionic liquids of low viscosity

Four of nine tetraalkylammonium-based amino-acid ionic liquids prepared in this work show lower viscosities than all amino acid-based ionic liquids found in the literature and their reversible CO(2) absorption approaches 0.5 mol per mol ionic liquid.     

Zwitterionic amino acids as precursors for nonmetal cation pentaborate salts

Nonmetal cation (NMC) pentaborate structures were synthesized using the amino acid molecules as cations precursors. Chemical composition analysis, infrared spectroscopy, mass analysis, boron nuclear magnetic resonance, and thermal gravimetric analysis (TGA/DTA) methods were used for structural characterization. The hydrogen storage efficiency of molecules was also determined experimentally. The recorded infrared spectra support the structural similarities of the molecules. Stretchings of pentaborate rings and characteristic peaks of amino acids were detected in infrared spectra. When the thermal analysis curves were recorded, it was found that the structures showed similar decomposition steps. Due to the result of thermal decay, glassy boron oxide (B₂O₃) formation was observed as the final decomposition products of all molecules. Peaks associated with boric acid, triborate, and pentaborate were observed in the ¹¹B spectra of these salts. Powder X-ray diffraction spectroscopy supports the presence of BO₃ and BO₄⁻ groups regarding the presence of pentaborate rings. It also indicates the high crystallinity of the structures. The molecular cavities detected by brunauer–emmett–teller analysis were found to be 3.586, 1.922, 1.673, and 1.923 g/cm³. Low-molecular cavities can be attributed to the high hydrogen-bonding capacity of the structures. The hydrogen capture efficiency of the pentaborate salts was found to be in the range of 0.039-0.     

Synthesis of aryl alkynyl carboxylic acids and aryl alkynes from propiolic acid and aryl halides by site selective coupling and decarboxylation

The coupling of propiolic acid with aryl iodides afforded the aryl alkynyl carboxylic acids and aryl alkynes in generally good yields. Aryl alkynyl carboxylic acids were obtained when the reaction was performed in the presence of Pd(PPh₃)₂Cl₂ (2.5 mol %), dppb (5.0 mol %) and DBU (5 equiv) at 50 °C. For the synthesis of the terminal aryl alkynes, the reaction was conducted in the presence of Pd(PPh₃)₂Cl₂ (2.5 mol %), dppb (5.0 mol %), DBU (5.0 equiv), and Cu(acac)₂ (10 mol %) at 25 °C for 5 h, and further reacted at 60 °C for 6 h.     

Synthesis and characterization of functionalized ferrocenylsilanes bearing a bulky substituent

Several types of overcrowded ferrocenylsilanes, Tbt(Fc)SiX₂(Tbt=2, 4, 6-tris[bis(trimethylsilyl)methyl]phenyl, Fc=ferrocenyl, X = H, OH, and Br) were synthesized and characterized. In addition, DFT calculations for ferrocenylsilanediol systems indicated the existence of the intramolecular hydrogen bonding between the Fe atom and H–O moiety in Tbt(Fc)Si(OH)₂. Dedicated to Professor Mitsuo Kira on the occasion of his 2005 Wacker Awardy     

Synthesis and characterization of new thiadiazole derivatives bearing a pyrazole moiety

A series of thidiazole derivatives (4, 7) from pyrazole-3-carboxylic acid chloride (2) and pyrazole-3,4-dicarboxylic acid chloride derivatives (6) were synthesized and characterized. The structures of the new compounds were confirmed byelemental analysis, NMR (¹H and ¹³C) and IR spectra. The molecular and crystal structure of 4-benzoyl-N-[5-(methylthio)-1,3,4-thiadiazol-2-yl]-1,5-di-phenyl-1H-pyrazole-3-carboxamide(4d)was determined by single crystal X-ray diffraction method.     

Synthesis of Z-alkenyl phosphorus compounds through hydroalumination and carbocupration of alkynyl precursors

The stereocontrolled synthesis of Z-alkenylphosphine-borane complexes is easily accomplished via the hydroalumination or carbocupration of alkynyl precursors. Z/E ratios are generally higher than 95/5. These reactions are stereocomplementary to our olefination approach.     

Synthesis of photolabile 2-(2-nitrophenyl)propyloxycarbonyl protected amino acids

The 2-(2-nitrophenyl)propyloxycarbonyl (NPPOC) group has been introduced as a photolabile amino protecting group for amino acids to be used as building blocks in photolithographic solid-phase peptide synthesis. NPPOC-protected amino acids were found to be cleaved in the presence of UV light about twice as fast as the corresponding o-nitroveratryloxycarbonyl (NVOC)-protected amino acids.     

Recognition of amino acids by functionalized calixarenes

The calixarenic receptors exhibit remarkable host-guest properties towards biologically relevant guests. Aspects of complex formation reactions between both native and derivatized amino acids, di-and tripeptides with calixarenic (chiral or not) receptors are summarized in this critical review. Thus, the discussions emphasize the parameters that affect the molecular binding selectivity and efficiency of functionalized calix[n]arenes towards these substrates. A brief survey on their application in separation of amino acids is also considered (123 references).     

Practical synthesis of functionalized terminal alkynes, 3,3,3-triethoxypropyne and ketal protected prop-2-ynones

Practical and economical synthesis of synthetically valuable 3,3,3-triethoxypropyne, ketal protected phenyl and methyl substituents prop-2-ynones is described. Bromination and subsequent 18-crown-6 catalyzed elimination of triethylorthoacrylate and ketal protected terminal alkenes with methyl and phenyl substituent which are inturn readily available from triethylorthopropionate, 3-chlorobutan-2-one and propiophenone afforded multigram quantities (>10?g) of corresponding functionalized terminal alkynes. Exploration of the synthetic utility of these alkynes is also demonstrated by the acetylenic substitution of the phenylalaninol derived 1,2-cyclic sulfamidate to deliver chiral alkynylated amines.     

Thiosemicarbazone salicylaldiminato palladium(II)-catalyzed alkynylation couplings between arylboronic acids and alkynes or alkynyl carboxylic acids

An efficient catalytic system has been developed for the synthesis of unsymmetrical substituted alkynes via the thiosemicarbazone salicylaldiminato palladium(II)-catalyzed alkynylation couplings between arylboronic acids and alkynes or alkynyl carboxylic acids under mild conditions.     

Iodination of organotrifluoroborates: synthesis of vinyl and alkynyl iodides

Vinyl- and alkynyltrifluoroborates are rapidly converted to vinyl and alkynyl iodides under mild conditions using sodium iodide in the presence of chloramine-T. The reaction is stereospecific and proceeds in excellent yield.     

Synthesis and biological activities of benzothiazole derivatives bearing a 1,3,4-thiadiazole moiety

A series of benzothiazole derivatives bearing a 1,3,4-thiadiazole moiety were designed, synthesized and evaluated for their antibacterial, antifungal and antiviral activities. The bioassay results indicated that most of target compounds showed good antiviral activities against tobacco mosaic virus (TMV) and antibacterial activities against Xanthomonas oryzae pv. oryzae (Xoo) and Ralstonia solanacearum (Rs). Especially, the anti-Xoo effect of title compounds 5k (N-(5-methoxybenzo[d]thiazol-2-yl)-2-((5-(2-tolyl)-1,3,4-thiadiazol-2-yl)thio)acetamide) and the anti-Rs effect of title compounds 5a (N-(5-nitrobenzo[d]thiazol-2-yl)-2-((5-(4-(trifluorom ethyl)phenyl)-1,3,4-thiadiazol-2-yl)thio)acetmide) respectively reached 52.4% and 71.6% at 100?µg/mL, which are superior to that of bismerthiazol (32.0% and 52.3%). In addition, the protective and inactivation activities of title compound 5i (N-(5-methoxybenzo [d]thiazol-2-yl)-2-((5-(4-nitrophenyl)-1,3,4-thiadiazol-2-yl)thio)acetamide) against TMV were 79.5% and 88.3%, respectively, which are better than that of ningnanmycin (76.4% and 86.8%). The above research showed that benzothiazole derivatives bearing a 1,3,4-thiadiazole moiety may be used as potential molecular templates in searching for highly-efficient antiviral and antibacterial agents.