Thuggacins, macrolide antibiotics active against Mycobacterium tuberculosis: isolation from myxobacteria, structure elucidation, conformation analysis and biosynthesis

Two novel antibiotics, thuggacin A (1) and B (2), were isolated from the myxobacterium Sorangium cellulosum. 1 and 2 are unique thiazole-containing macrolides with side chains on both sides of the lactone group. Upon standing in solution, thuggacin A (1) rearranges by acyl migration of the lactone group to give a mixture with thuggacins B (2) and C (3). NOEs and vicinal coupling constants within the lactone ring provided distinct data for the generation of a structure model by PM3 calculations, which allowed an analysis of the conformation in solution and the relative configuration of six asymmetric centres. A minor sorangium metabolite was identified as 13-methyl-thuggacin A (4). Furthermore, two natural thuggacin variants, 5 and 6, were found in another myxobacterium, Chondromyces crocatus. In these variants, one side chain is replaced by a methyl group and a hydroxy group is repositioned to give a primary alcohol at the former methyl site, in an alpha position with respect to the thiazole ring. 1 proved to be active against clinical isolates and reference strains of Mycobacterium tuberculosis. Preliminary studies on the mechanism of action indicate inhibition of the cellular electron-transport chain.     

ENHANCEMENT OF ENERGY TRANSFER FROM THE TERMINAL CHROMOPHORE OF POLYETHER TO EUROPIUM CATION(Ⅲ)VIA COMPLEXATION

The fluorescence spectra of naphthalene end-labelled polyethylene glycol)(N-P_nN) in methanol solution in the presence of europium cation(Ⅲ) was investigated. Selective excitation of the naphthalene group of N-P_n-N re-sults in the emission of europium cation. suggesting that the polyether chain complexes with europium cation, thus efficient energy transfer from naphthalene chromophore to europium cation occurs. Photoirradiation of N-P-N in solution leads to intramolecular dimerization of the two terminal naphthalene groups to give a crown ether. The complexation of this photochemically synthesized crown ether and europium cation was also studied.     

钯催化下共轭二烯二炔官能团的构成

制备了一系列共轭烯炔化合物以及卤代烯炔化合物,并利用它们在钯催化下交叉偶联构成了与环戊烯共轭骈连的烯二炔即共轭的二烯二炔结构。此结构为抗肿瘤抗生素C-1027发色团和kedarcidin发色团所共有;同时探讨了它们在钯催化下交叉偶连的性质,发现共轭的卤代烯炔与共轭的端炔交叉偶连的趋势为:碘代烯>溴代烯>氯代烯。     

Elastomeric polyurethanes modified with geminal bisphosphonate groups

Three types of elastomeric segmented polyurethanes represented by a polyether‐urethane, a polyurethane‐urea, and a polycarbonate‐urethane were introduced into a modified low‐temperature variant of base‐induced N‐alkylation of urethane hard segments with an excess of 1,6‐dibromohexane in N,N′‐dimethylacetamide (DMAc), resulting in the modification of polymers with 0.08–0.26 mmol/g of pendant 6‐bromohexyl groups. Either lithium diisopropylamide (LDA) or sodium hydride was used to initiate the reaction, although LDA was found to be more suitable for the bromoalkylation. Selected bromoalkylated polyurethanes of all three types were reacted with thiol‐containing bisphosphonates, to yield the polymers modified with 0.08–0.12 mmol/g of geminal nonesterified covalently attached bisphosphonate groups. Two thiol‐containing geminal bisphosphonates used in the modifications were prepared via reactions of nucleophilic addition to vinylidene‐bisphosphonic acid. All three types of polyurethanes were found equally suitable for the modifications. The bisphosphonate‐modified polyurethanes with nonmetallic cations on the bisphosphonate groups remain soluble in the solvents suitable for the dissolution of nonmodified polymers and can be processed into films by solvent casting. After the exchange of nonmetallic cations to sodium, the polymers become insoluble in any solvent, probably as a result of the intermolecular coordination of bisphosphonate groups with the metal cations. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 105–116, 2001     

An NMR investigation of the interaction of polyethylene oxide with water‐soluble poly(vinyl phenol‐co‐potassium styrene sulfonate)

The water‐soluble complex of polyethylene oxide (PEO) with poly (vinyl phenol‐co‐potassium styrene sulfonate) (PVPh‐co‐KSS) was studied by liquid‐state NMR. PEO showed two peaks in the ¹H spectra, which corresponded to the free and complexed PEO. The ratio of the free PEO/complexed PEO was decreased with the increase in the mixing ratio of PVPh‐co‐KSS/PEO. Some of the complex formation disappeared when the pH was raised from 6.4 to 12.0. It had been thought that at high pH, the phenolic groups dissociate and thus cannot form hydrogen bonds. The fact that NMR indicates some interaction at pH 12.0 implies there are some other interactions, such as hydrophobic interactions between the aromatic rings and the polyether methylene groups, contributing to PEO and PVPh‐co‐KSS complex formation. Nuclear Overhauser effect (NOE) cross peaks were observed between PEO and the aromatic protons of PVPh‐co‐KSS in nuclear Overhauser effect spectra (NOESY) suggesting that the distance between PEO and the aromatic protons of PVPh‐co‐KSS was less than 5 Å. The exchange between the complexed PEO and the free PEO was slow on the NMR time scale. The ratio of the integral of the complexed PEO to the free PEO increased with temperature, indicating that the number of PEO segments interacting with the aromatic ring increases with temperature. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1276–1284, 2000     

Simultaneous construction of a polyether backbone and a variety of keto side chains by three‐component polycondensation: An improved method for the use of a variety of silyl enol ethers

For the synthesis of polyethers with a variety of keto side chains in a one‐step reaction, the three‐component polycondensation of dialdehydes, diol disilyl ethers, and silyl enol ethers of ketones was investigated. The method of monomer addition strongly affected the molecular weight of polymers and was optimized to yield high molecular weight polymers by model reactions. A variety of dialdehydes, diol disilyl ethers, and silyl enol ethers were polymerized in the presence of a catalytic amount of triphenylmethyl (trityl) perchlorate in CH₂Cl₂ at −78 °C according to the method of monomer addition. This polymer synthesis was unusual in that it concurrently constructed both the polyether backbone and the keto side chains from three starting compounds. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 179–188, 2000     

Preparation of new polyether with oxetane pendant group

A new oxetane-containing polyether was synthesized by polycondensation of bisphenol-AF (BPAF) with 3,3-bis(chloromethyl)oxetane (BCMO) using the phase-transfer catalyzed method. The polycondensation proceeded very smoothly in aromatic solvents, catalyzed by quaternary ammonium or phosphonium salts, such as tetrabutylammonium bromide (TBAB) and tetrabutylphosphonium bromide (TBPB), to afford the polymer with high yield and molecular weight. Further, a polymer with relatively high molecular weight was obtained when the reactions were carried out in aromatic and lipophilic solvents such as benzene and nitrobenzene. The modification of this oxetane-containing polyether was easily achieved by carrying out ring-opening of the oxetane ring by using hydrogen chloride in methylene chloride, which produced a functional polymer containing hydroxyl and chloro groups. The oxetane-containing polyether was observed to be soluble in chlorinated aliphatic hydrocarbons such as methylene chloride and chloroform, as well as polar solvents such as DMSO, DMF, and DMAc, and also some common organic solvents such as benzene and toluene. However, it was insoluble in both aliphatic hydrocarbons as well as alcoholic solvents. The oxetane-containing polyether was observed to start losing weight at around 300°C under nitrogen atmosphere, and 10% weight loss was measured to be 411°C. The glass transition temperature of the oxetane-containing polyether was measured to be 134°C and the wide-angle X-ray diffraction pattern revealed this polymer to be semicrystalline. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 103–107, 1998     

Thermosensitive lactitol-based polyether polyol (LPEP) hydrogels

A series of new thermosensitive polymer hydrogels were prepared by reacting acylated poly(ethylene glycol) bis(carboxymethyl) ether (PEGBCOCl) with lactitol-based polyether polyols (LPEP). The polyether polyols were generated from propoxylation of lactitol and have molecular weights ranging from 1337 to 4055 g/mol. The hydrogels absorb water up to 1000% of their dry weight and expel free water at temperatures at and above 30°C. The wide ranging swelling behavior and excellent thermosensitivity depend closely on the degree of crosslinking and the propylene oxide lengths in the polyols. Differential scanning calorimetry of the hydrogels showed two endotherms associated with the phase transitions of PO and EO segments in the hydrogel structures. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 979–984, 1998     

Open spaces and molecular motions of polyether-based network polymers probed by positron annihilation

The lifetimes of positrons have been measured for network polymers based on polyethers. From the temperature dependence of the lifetime of ortho-positronium (o-Ps), τ₃, for the network polymer of poly(ethylene oxide-co-propylene oxide) [P(EO/PO)], an onset temperature for limited local motions of molecules, T_γ, and the glass transition temperature, T_g, were determined to be 57 and 201 K, respectively. For the network polymer of poly[EO-co-2-(2-methoxyethoxy)ethyl glycidyl ether] [P(EO/MEEGE)], T_γ and T_g were determined to be 57 and 185 K, respectively. For both specimens, above 270 K, the observed linear temperature dependence of τ₃ was attributed to the thermal expansion of open spaces in a liquid state. In the temperature range between T_γ and 270 K, for the P(EO/MEEGE) network, τ₃ was longer and its intensity was smaller than those for the P(EO/PO) network. These results were attributed to the increase in the size of open spaces for the P(EO/MEEGE) network polymer and the blocking of these regions by motions of side chains and chain ends. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 1919–1925, 1998