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新型糖氨基酸类化合物的合成研究
(2015)
Sugar amino acids (SAAs) are carbohydrate derivatives bearing both amino and carboxylic acid functional groups. SAAs represent an important class of multifunctional building blocks, which are amenable to serve as glycomimetics or peptidomimetics with well-defined structures and useful properties. Because SAAs exist in nature in many forms with various biological activities, recently, many unnatural SAAs, as the demand for finding new molecules to discover new drugs and new materials, have been designed and synthesized by a number of research groups. In this paper, we have developed a convenient method for the synthesis of novel SAAs gluco-7 and galacto-7 for the first time. The structure of gluco-7 was similar to the natural SAA glucosaminuronic acid that was a component of many typical bacterial cell walls and could be used for the preparation of type D flu vaccine; while galacto-7 was similar to the natural SAA galactosaminuronic acid that was one of bacterial Vi-antigen components of Escherichia coli. Starting from unexpensive and commercially available 3,4,6-tri-O-acetyl-D-glucal and 3,4,6-tri-O-acetyl-D-galactal, two novel SAAs gluco-7 and galacto-7 were achieved in the linear 6 steps with 34% overall yield and 19% overall yield, respectively. The key reactions included radical addition, decarboxylation, iodine generation reaction, azide reaction and reductive amination reaction. The crucial step was the synthesis of the target compound gluco-7 from gluco-6. By using method A, the target compound gluco-7 was obtained in 4 steps with 63% overall yield. To optimize the transformation from gluco-6 to gluco-7, method B was developed to generate gluco-7 by using one-pot reaction successfully with 76% yield only in one step. It proved that method B was superior to method A with shorter steps and higher yields. All the new compounds were characterized by IR, H-1 NMR, C-13 NMR and HRMS data. Study on the synthesis and biological evaluation of linear and cyclic oligomers derived from gluco-7 and galacto-7 are currently in progress.
In diesem Artikel werden die Synthese von Thymolblau als Schülerexperiment und passende Augmented-Reality (AR)-gestützte Lernmaterialien vorgestellt. Zudem wird der Kenntnisstand zur Synthese von Thymolblau sowie dessen pH-abhängige Struktur-Eigenschafts-Beziehung vor dem Hintergrund neuerer Erkenntnisse diskutiert und es wird über Erfahrungen mit dem Einsatz des Experimentes in der schulischen und universitären Praxis und im Rahmen von Fortbildungen berichtet.
Dumortierite was synthesized in piston-cylinder experiments at 2.5-4.0 GPa, 650-700 degrees C in the Al2O3 -B2O3-SiO2-H2O (ABSH) system. Electron-microprobe (EMP) analyses reveal significant boron-excess (up to 0.26 B-[4] per formula unit, pfu) and silicon-deficiency relative to the ideal anhydrous dumortierite stoichiometry Al7BSi3O18 . The EMP data in conjunction with results from single-crystal Raman spectroscopy and powder X-ray diffraction provide evidence that silicon at the tetrahedral site is replaced by excess boron via the substitution Si-[4] <--> B-[4] + H. The Raman spectrum of synthetic dumortierite in the frequency region 2000 4000 cm(-1) comprises eight bands, of which six are located at frequencies below 3400 cm(-1). This points to strong hydrogen bonding, most likely O2-H center dot center dot center dot O7 and O7-H center dot center dot center dot O2, arising from a high number of octahedral vacancies at the All site and substitution of trivalent Al3+ and B3+ for Si4+ at Si1 and Si2 sites, causing decreasing acceptor-donor distances and lower incident valence at the acceptor oxygen. Contrary to the synthetic high-pressure ABSH-dumortierite, magnesiodumortierite from the Dora-Maira Massif, which is assumed to have formed at similar conditions (2.5-3.0 GPa, 700 degrees C), does not show any B-excess. Tourmaline shows an analogous behaviour in that magnesium-rich (e.g., dravitic) tourmaline formed at high pressure shows no or only minor amounts of tetrahedral boron, whereas natural aluminum-rich tourmaline and synthetic olenitic tourmaline formed at high pressures can incorporate significant amounts of tetrahedral boron. Two mechanisms might account for this discrepancy: (i) Structural avoidance of Mg-[6]-(OR3+)-R-[4] configurations in magnesiodumortierite due to charge deficieny at the oxygens O2 and O7 and strong local distortion of M1 due to decreased O2-O7 bond length, and/or (ii) decreasing fluid mobility of boron in Al-rich systems at high pressures.
Two approaches for the synthesis of prenylated isoflavones were explored: the 2,3-oxidative rearrangement/cross metathesis approach, using hypervalent iodine reagents as oxidants and the Suzuki-Miyaura cross-coupling/cross metathesis approach. Three natural prenylated isoflavones: 5-deoxy-3′-prenylbiochanin A (59), erysubin F (61) and 7-methoxyebenosin (64), and non-natural analogues: 7,4′-dimethoxy-8,3′-diprenylisoflavone (126j) and 4′-hydroxy-7-methoxy-8,3′-diprenylisoflavone (128) were synthesized for the first time via the 2,3-oxidative rearrangement/cross metathesis approach, using mono- or diallylated flavanones as key intermediates. The reaction of flavanones with hypervalent iodine reagents afforded isoflavones via a 2,3-oxidative rearrangement and the corresponding flavone isomers via a 2,3-dehydrogenation. This afforded the synthesis of 7,4′-dimethoxy-8-prenylflavone (127g), 7,4′-dimethoxy-8,3′-diprenylflavone (127j), 7,4′-dihydroxy-8,3′-diprenylflavone (129) and 4′-hydroxy-7-methoxy-8,3′-diprenylflavone (130), the non-natural regioisomers of 7-methoxyebenosin, 126j, erysubin F and 128 respectively. Three natural prenylated isoflavones: 3′-prenylbiochanin A (58), neobavaisoflavone (66) and 7-methoxyneobavaisoflavone (137) were synthesized for the first time using the Suzuki-Miyaura cross-coupling/cross metathesis approach. The structures of 3′-prenylbiochanin A (58) and 5-deoxy-3′-prenylbiochanin A (59) were confirmed by single crystal X-ray diffraction analysis. The 2,3-oxidative rearrangement approach appears to be limited to the substitution pattern on both rings A and B of the flavanone while the Suzuki-Miyaura cross-coupling approach appears to be the most suitable for the synthesis of simple isoflavones or prenylated isoflavones whose prenyl substituents or allyl groups, the substituents that are essential precursors for the prenyl side chains, can be regioselectively introduced after the construction of the isoflavone core.
The chalcone-flavanone hybrids 146, 147 and 148, hybrids of the naturally occurring bioactive flavanones liquiritigenin-7-methyl ether, liquiritigenin and liquiritigenin-4′-methyl ether respectively were also synthesized for the first time, using Matsuda-Heck arylation and allylic/benzylic oxidation as key steps.
The intermolecular interactions of 5-deoxy-3′-prenylbiochanin A (59) and its two closely related precursors 106a and 106b was investigated by single crystal and Hirshfeld surface analyses to comprehend their different physicochemical properties. The results indicate that the presence of strong intermolecular O-H···O hydrogen bonds and an increase in the number of π-stacking interactions increases the melting point and lowers the solubility of isoflavone derivatives. However, the strong intermolecular O-H···O hydrogen bonds have a greater effect than the π-stacking interactions.
5-Deoxy-3′-prenylbiochanin A (59), erysubin F (61) and 7,4′-dihydroxy-8,3′-diprenylflavone (129), were tested against three bacterial strains and one fungal pathogen. All the three compounds were inactive against Salmonella enterica subsp. enterica (NCTC 13349), Escherichia coli (ATCC 25922), and Candida albicans (ATCC 90028), with MIC values greater than 80.0 μM. The diprenylated isoflavone erysubin F (61) and its flavone isomer 129 showed in vitro activity against methicillin-resistant Staphylococcus aureus (MRSA, ATCC 43300) at MIC values of 15.4 and 20.5 μM, respectively. 5-Deoxy-3′-prenylbiochanin A (59) was inactive against this MRSA strain. Erysubin F (61) and its flavone isomer 129 could serve as lead compounds for the development of new alternative drugs for the treatment of MRSA infections.
The structures and synthesis of polyzwitterions ("polybetaines") are reviewed, emphasizing the literature of the past decade. Particular attention is given to the general challenges faced, and to successful strategies to obtain polymers with a true balance of permanent cationic and anionic groups, thus resulting in an overall zero charge. Also, the progress due to applying new methodologies from general polymer synthesis, such as controlled polymerization methods or the use of "click" chemical reactions is presented. Furthermore, the emerging topic of responsive ("smart") polyzwitterions is addressed. The considerations and critical discussions are illustrated by typical examples.
The structures and synthesis of polyzwitterions ("polybetaines") are reviewed, emphasizing the literature of the past decade. Particular attention is given to the general challenges faced, and to successful strategies to obtain polymers with a true balance of permanent cationic and anionic groups, thus resulting in an overall zero charge. Also, the progress due to applying new methodologies from general polymer synthesis, such as controlled polymerization methods or the use of "click" chemical reactions is presented. Furthermore, the emerging topic of responsive ("smart") polyzwitterions is addressed. The considerations and critical discussions are illustrated by typical examples.
Natural products have proved to be a major resource in the discovery and development of many pharmaceuticals that are in use today. There is a wide variety of biologically active natural products that contain conjugated polyenes or benzofuran structures. Therefore, new synthetic methods for the construction of such building blocks are of great interest to synthetic chemists. The recently developed one-pot tethered ring-closing metathesis approach allows for the formation of Z,E-dienoates in high stereoselectivity. The extension of this method with a Julia-Kocienski olefination protocol would allow for the formation of conjugated trienes in a stereoselective manner. This strategy was applied in the total synthesis of conjugated triene containing (+)-bretonin B. Additionally, investigations of cross metathesis using methyl substituted olefins were pursued. This methodology was applied, as a one-pot cross metathesis/ring-closing metathesis sequence, in the total synthesis of benzofuran containing 7-methoxywutaifuranal. Finally, the design and synthesis of a catalyst for stereoretentive metathesis in aqueous media was investigated.
Radical addition fragmentation chain transfer (RAFT) polymerization of ferrocenyl (meth)acrylates
(2012)
We report on the controlled free radical homopolymerization of 1-ferrocenylethyl acrylate as well as of three new ferrocene bearing monomers, namely 4-ferrocenylbutyl acrylate, 2-ferrocenylamido-2-methylpropyl acrylate, and 4-ferrocenylbutyl methacrylate, by the RAFT technique. For comparison, the latter monomer was polymerized using ATRP, too. The ferrocene containing monomers were found to be less reactive than their analogues free of ferrocene. The reasons for the low polymerizability are not entirely clear. As the addition of free ferrocene to the reaction mixture did not notably affect the polymerizations, sterical hindrance by the bulky ferrocene moiety fixed on the monomers seems to be the most probable explanation. Molar masses found for 1-ferrocenylethyl acrylate did not exceed 10,000 g mol(-1), while for 4-ferrocenylbutyl (meth) acrylate molar masses of 15,000 g mol(-1) could be obtained. With PDIs as low as 1.3 in RAFT polymerization of the monomers, good control over the polymerization was achieved.
Point-of-care and in-vivo bio-diagnostic tools are the current need for the present critical scenarios in the healthcare industry. The past few decades have seen a surge in research activities related to solving the challenges associated with precise on-site bio-sensing. Cutting-edge fiber optic technology enables the interaction of light with functionalized fiber surfaces at remote locations to develop a novel, miniaturized and cost-effective lab on fiber technology for bio-sensing applications. The recent remarkable developments in the field of nanotechnology provide innumerable functionalization methodologies to develop selective bio-recognition elements for label free biosensors. These exceptional methods may be easily integrated with fiber surfaces to provide highly selective light-matter interaction depending on various transduction mechanisms. In the present review, an overview of optical fiber-based biosensors has been provided with focus on physical principles used, along with the functionalization protocols for the detection of various biological analytes to diagnose the disease. The design and performance of these biosensors in terms of operating range, selectivity, response time and limit of detection have been discussed. In the concluding remarks, the challenges associated with these biosensors and the improvement required to develop handheld devices to enable direct target detection have been highlighted.