High-performance liquid chromatographic separation of subcomponents of antimycin A

Using a reversed-phase high-performance liquid chromatographic (HPLC) technique, a mixture of antimycins A was separated into eight hitherto unreported subcomponents, A1a, A1b, A2a, A2b, A3a, A3b, A4a, and A4b. Although a base-line resolution of the known four major antimycins A1, A2, A3, and A4 was readily achieved with mobile phases containing acetate buffers, the separation of the new antibiotic subcomponents was highly sensitive to variation in mobile phase conditions. The type and composition of organic modifers, the nature of buffer salts, and the concentration of added electrolytes had profound effects on capacity factors, separation factors, and peak resolution values. Of the numerous chromatographic systems examined, a mobile phase consisting of methanol-water (70:30) and 0.005 M tetrabutylammonium phosphate at pH 3.0 yielded the most satisfactory results for the separation of the subcomponents. Reversed-phase gradient HPLC separation of the dansylated or methylated antibiotic compounds produced superior chromatographic characteristics and the presence of added electrolytes was not a critical factor for achieving separation. Differences in the chromatographic outcome between homologous and structural isomers were interpreted based on a differential solvophobic interaction rationale. Preparative reversed-phase HPLC under optimal conditions enabled isolation of pure samples of the methylated antimycin subcomponents for use in structural studies.     

Bioinspired total synthesis of agelastatin A

A one-two punch: two potentially biosynthetically relevant cyclizations of a keramadine analogue give agelastatin A. A diastereoselective C-ring formation, which proceeds through a 5-exo-trig cyclization or a Nazarov cyclization of a red-colored N-acyliminium intermediate, generates the three contiguous stereocenters of the cyclopentane core. A silica gel assisted cyclization of a nagelamide J analogue gives agelastatin A.     

A correlated force-optical study on the self-assembly behavior of annexin V on model membranes: effect of dye conjugation

We have examined the self-assembled membrane-bound aggregates of two annexin V (A5) dye conjugates and compared them to those from native A5. Native A5 and FITC-labeled A5 (A5-FITC) both formed discrete well-defined crystalline monolayer domains of p6 symmetry. However, A5-FITC also showed additional domains with a corrugated appearance not observed in native A5. In contrast, Cy3-labeled A5 (A5-Cy3) showed a mixture of crystalline monolayer and irregular multilayered domains, with the ratio of the two types varying significantly from sample to sample, and also required a much longer incubation time than native A5 and A5-FITC. When A5-FITC and A5-Cy3 were co-incubated on the same bilayer, well-defined crystalline monolayer domains containing both A5-FITC and A5-Cy3 were consistently observed at a much shorter incubation time than that of pure A5-Cy3 alone, indicating that A5-FITC facilitates the inclusion of A5-Cy3. These results suggest that dye labels can affect A5 2D self-assembly and crystal formation on membrane surfaces.     

Thin-layer chromatographic study of the metabolites of erythromycins in the Wistar rat

The metabolites of erythromycin A, anhydroerythromycin A, N-demethylerythromycin A and erythromycin B in the Wistar rat were studied by thin-layer chromatography. In some experiments germ-free rats, rats with a cannulated bile duct and a gastrectomized rat were used. The erythromycins examined were shown to undergo two principal changes, N-demethylation and acid-catalysed degradation. It was demonstrated that the stomach and the liver are not the sole sites of acid degradation and demethylation of erythromycins, respectively. Erythromycin A gives three principal metabolites, anhydroerythromycin A, anhydro-N-demethylerythromycin A and N-demethylerythromycin A, and erythromycin A enol ether and N-demethylerythromycin A enol ether are present to a minor extent. 5-O-Desosaminylerythronolide A was also identified, suggesting the presence of an erythromycin glycosidase.     

Synthesis and evaluation of adenosine antagonist activity of a series of [1,2,4]triazolo[1,5-c]quinazolines

A series of [1,2,4]triazolo[1,5-c]quinazolines were prepared in satisfactory yields by reaction of some derivatives of 2-aminobenzohydrazide with several hydrochlorides of aromatic amidines, and their binding affinities for the recombinant human adenosine A2A and A2B receptors were determined. None of the new compounds showed noteworthy affinity for these receptors, though a very high affinity for the A2A receptor and, consequently, a high level of A2A/A2B selectivity was revealed for one of the synthesized compounds.     

Decomposition of dinuclear manganese complexes for the preparation of nanostructured oxide materials

The crystal structures of several dinuclear complexes of manganese are reported, and the decomposition and analysis of the nanostructured products derived from them are presented. 1,4,7,10-Tetraazacyclododecane (cyclen) forms dinuclear complexes 1-4 containing doubly oxo-bridged or oxo-acetato bridging ligands depending on the manganese salt used for the reaction. Doubly oxo-bridged 1 crystallizes in the orthorhombic space group Pnma, a = 22.3850(14) A, b = 9.1934(5) A, c = 13.2424(10) A, V = 2725.2(3) A(3). 2, containing [Mn(SCN)5](3-) conteranions, crystallizes in monoclinic space group I2/a with a = 18.2699(10) A, b = 11.2384(6) A, c = 18.6432(9) A, alpha = 90.00 degrees, beta = 114.510(6) degrees, gamma = 90.00 degrees, V = 3483.0(3) A(3). Oxo-acetato-bridged 3 crystallizes in orthorhombic space group Pca21, a = 13.9322(11) A, b = 16.2332(13) A, c = 14.6794(8) A, V = 3320.0(4) A(3). Compound 4 consists of a templated quasi-one-dimensional manganese oxalate crystallized in the triclinic space group P1, a = 9.5442(11) A, b = 10.3758(10) A, c = 21.851(2) A, alpha = 83.720(12) degrees, beta = 80.106(13) degrees, gamma = 85.457(13) degrees, V = 2114.9(4) A(3). Compounds 1, 3, and 4 decompose to nanostructured oxide materials, which may be isolated in bulk as lamellar-structured particles or microspheres or deposited on substrates.     

Innate immune responses of synthetic lipid A derivatives of Neisseria meningitidis

Differences in the pattern and chemical nature of fatty acids of lipid A of Neisseria meningitides lipooligosaccharides (LOS) and Escherichia coli lipopolysaccharides (LPS) may account for differences in inflammatory properties. Furthermore, there are indications that dimeric 3-deoxy-D-manno-oct-2-ulosonic acid (KDO) moieties of LOS and LPS enhance biological activities. Heterogeneity in the structure of lipid A and possible contaminations with other inflammatory components have made it difficult to confirm these observations. To address these problems, a highly convergent approach for the synthesis of a lipid A derivative containing KDO has been developed, which relies on the ability to selectively remove or unmask in a sequential manner an isopropylidene acetal, 9-fluorenylmethoxycarbonyl (Fmoc), allyloxycarbonate (Alloc), azide, and thexyldimethylsilyl (TDS) ether. The strategy was employed for the synthesis of N. meningitidis lipid A containing KDO (3). Mouse macrophages were exposed to the synthetic compound and its parent LOS, E. coli lipid A (2), and a hybrid derivative (4) that has the asymmetrical acylation pattern of E. coli lipid A, but the shorter lipids of meningococcal lipid A. The resulting supernatants were examined for tumor necrosis factor alpha (TNF-alpha) and interferon beta (IFN-beta) production. The lipid A derivative containing KDO was much more active than lipid A alone and just slightly less active than its parent LOS, indicating that one KDO moiety is sufficient for full activity of TNF-alpha and IFN-beta induction. The lipid A of N. meningitidis was a significantly more potent inducer of TNF-alpha and IFN-beta than E. coli lipid A, which is due to a number of shorter fatty acids. The compounds did not demonstrate a bias towards a MyD88- or TRIF-dependent response.     

Total synthesis of the cyclodepsipeptide apratoxin A and its analogues and assessment of their biological activities

A novel total synthesis of apratoxin A is described, with key steps including the assembly of its ketide segment through a D-proline-catalyzed direct aldol reaction and Oppolzer's anti aldol reaction and the preparation of its thiazoline unit in a biomimetic synthesis. An oxazoline analogue of apratoxin A has also been elaborated by a similar approach. This compound has a potency against HeLa cell proliferation only slightly lower than that of apratoxin A, whilst a C(40)-demethylated oxazoline analogue of apratoxin A displays a much lower cytotoxicity and the C(37)-epimer and C(37) demethylation product of this new analogue are inactive. These results suggest that the two methyl groups at C(37) and C(40) and the stereochemistry at C(37) are essential for the potent cellular activity of the oxazoline analogue of apratoxin A. Further biological analysis revealed that both synthetic apratoxin A and its oxazoline analogue inhibited cell proliferation by causing cell cycle arrest in the G1 phase.     

A high-copy-number plasmid capable of replication in thermophilic cyanobacteria

A 2.5 kb high-copy-number plasmid, pM A4 in thermophilic cyanobacterium Synechococcus sp. M A4 was isolated and characterized to develop a genetic engineering system for thermophilic cyanobacteria. The copy number of pM A4 was determined to be by densitometry about 350/cell. The pM A4 may be a type of rolling-circle plasmid, because a possible rep gene encoding 34 k D-protein and a consensus sequence of a double-stranded origin nick site of rolling circle plasmids were found in the pM A4 sequence. The pM A4 was electro-introduced into another thermophile, Synechococcus sp. MA 19, which is the strongest poly-β-hydroxybutyrate (PHB) accumulator in photoau totrophic organisms. The pM A4 was incorporated and retained in MA 19. These results indicate that pM A4 could be developed as a useful vector for thermophilic cyanobacteria.     

Synthesis of Arcyriarubin A and Arcyriaflavin A via Cross-Coupling of Indolylboronic Acid with Dibromomaleimides

Arcyriarubin A was first isolated by Steglich in 1980; it is also the key intermediate in the synthesis of indolocarbazole compounds. A new synthetic approach to the natural products arcyriaflavin A and arcyriarubin A is described. The key step is a Suzuki cross-coupling reaction using indolylboronic acid as the starting material. The preparation of arcyriaflavin A was accomplished in eight steps from indole for a total yield of 21%.     

Early Divergence in Misfolding Pathways of Amyloid-Beta Peptides

The amyloid cascade hypothesis proposes that amyloid-beta (Aβ) aggregation is the initial triggering event in Alzheimer's disease. Here, we utilize NMR spectroscopy and monitor the structural dynamics of two variants of Aβ, Aβ40 and Aβ42, as a function of temperature. Despite having identical amino acid sequence except for the two additional C-terminal residues, Aβ42 has higher aggregation propensity than Aβ40. As revealed by the NMR data on dynamics, including backbone chemical shifts, intra-methyl cross-correlated relaxation rates and glycine-based singlet-states, the C-terminal region of Aβ, especially the G33-L34-M35 segment, plays a particular role in the early steps of temperature-induced Aβ aggregation. In Aβ42, the distinct dynamical behaviour of C-terminal residues at higher temperatures is accompanied with marked changes in the backbone dynamics of residues V24-K28. The distinctive role of the C-terminal region of Aβ42 in the initiation of aggregation defines a target for the rational design of Aβ42 aggregation inhibitors.     

Concanavalin A perturbation of membrane enzymes of mammary gland.

The plant lectin concanavalin A (Con A) specifically inactivates the 5'-nucleotidase of a plasma membrane-enriched fraction from lactating mammary gland. The lectin also causes an activation of the membrane Mg++-ATPase, but does not affect galactosyltransferase or alkaline phosphatase. The enzyme perturbations are prevented by alpha-methylmannoside, an inhibitor of Con A binding, indicating that specific binding to carbohydrate structures rather than nonspecific protein-protein interaction is involved. Solubilization of the 5'-nucleotidase in detergents (0.2% Triton X-100 or 1% deoxycholate) does not prevent Con A inactivation, indicating that incorporation into the membrane structure is not a requirement for the Con A effect. the results suggest that Con A inactivates the 5'-nucleotidase by a direct interaction with the enzyme and that this enzyme is a Con A receptor site on the surface of mammary cells.     

Synthesis and characterization of zirconogermanates

Six new zirconogermanates have been prepared under hydrothermal conditions using amines as bases. There are four new structure types (ASU-n) with a common motif of ZrGe(5). ASU-23 is a layered structure: ZrGe(3)O(8)(OH)F.[C(10)H(26)N(4)].H(2)O, space group P2(1)/n, a = 6.7957(8) A, b = 12.700(1) A, c = 24.293(3) A, beta = 97.936(2) degrees, V = 2076.4(4) A(3). ASU-24 is a pillared layered structure: Zr(3)Ge(6)O(18)(OH(2),F)(4)F(2).[C(6)H(18)N(2)].[C(6)H(17)N(2)](2).2H(2)O, space group P2(1)/n, a = 7.4249(3) A, b = 25.198(1) A, c = 11.3483(5) A, beta = 90.995(1) degrees, V = 2122.9(2) A(3). This material has the lowest framework density (FD) of any oxide material that we are aware of (FD = 8.48 metal atoms/nm(3)). Two other materials form three-dimensional open-frameworks, ASU-25: ZrGe(3)O(9).[C(3)H(12)N(2)], space group P112(1)/a, a = 13.1994(4) A, b = 7.6828(2) A, c = 11.2373(3) A, gamma = 91.233(3) degrees, V = 1139.29(5) A(3). The other is ASU-26: ZrGe(3)O(9).[C(2)H(10)N(2)], space group Pn, a = 13.7611(3) A, b = 7.7294(2) A, c = 11.2331(3) A, beta = 104.793(1) degrees, V = 1155.21(4) A(3). ASU-25 is related to the mineral umbite K(2)ZrSi(3)O(9).H(2)O. The germanium equivalent has been prepared through the inorganic route: K(2)ZrGe(3)O(9).H(2)O, space group P2(1)2(1)2(1), a = 13.6432(6) A, b = 7.4256(3) A, c = 10.3973(4) A, V = 1053.33(8) A(3). The structural relationships between ASU-25 and its inorganic counterpart are described. The thermal decomposition of the germanium umbite generated the cyclic trigermanate K(2)ZrGe(3)O(9), analogue of the mineral wadeite, crystallizing in the orthorhombic system, a = 7.076 A, b = 12.123 A, c = 10.451 A, V = 904.5 A(3).     

Unexpected formation of an azetidine-carborane derivative by dehydration of N-(1,12-dicarba-closo-dodecaboran-1-yl)formamide. The first X-ray structure of a 2,3-bis(imino)azetidine

Efforts to dehydrate (1,12-dicarba-closo-dodecaboran(12)-1-yl)formamide (a = 6.685(2) A, b = 12.877(4) A, c = 12.547(4) A, alpha = gamma = 90 degrees, beta = 90.724(11) degrees, V = 1080.8(6) A(3), Z = 4) resulted in the formation of a series of unexpected products. Addition of the Burgess reagent to the formamide, for example, led to the isolation of the corresponding methyl carbamate (a = 11.529(8) A, b = 11.529(8) A, c = 11.402(12) A, alpha = beta = gamma = 90 degrees, V = 1516(2) A(3), Z = 4), while treatment with triphosgene, a well-known dehydrating agent, resulted in the formation of a highly unusual 2,3-bis(p-carboranylimino)azetidine derivative. This particular compound, in the presence of Re(I), was hydrolyzed to give the corresponding amide, which is the first example of a 2,3-bis(imino)azetidine that has been characterized crystallographically (a = 38.496(13) A, b = 11.920(4) A, c = 27.523(10) A, beta = 127.050(5) degrees, V = 10079(6) A(3), Z = 8).     

Matrix-Assisted Laser Desorption Mass Spectrometry of Biotransformation Products of Dynorphin A in Vitro

The utility of matrix-assisted laser desorption mass spectrometry for characterizing products of in vitro processing of synthetic dynorphin A (Dyn A) peptides in biologic matrices is described. A series of laser desorption matrices were tested for their response to Dyn A (1–6), Dyn A (1–7), Dyn A (1–8), Dyn A (1–9), Dyn A (1–l0), Dyn A (1–13), Dyn A (2-17), and Dyn A (1–17). α-Cyano-4-hydroxycinnamic acid was chosen as a suitable matrix for subsequent studies. Mass spectra of dynorphin peptides indicated a good signal-to-noise response down to (1) 10 fmole of Dyn A (1–10) amide standard in aqueous acidic solution and (2) a concentration of 10^-7 M for seven dynorphin peptides spiked into human plasma. Two examples of the mass spectrometric analysis of the products of in vitro processing are presented: Dyn A (1–13) and Dyn A (1–17) in human blood. The presence and identity of processed peptides can be simply inferred from the molecular masses provided by the mass spectrometric measurement without extensive sample purification. A comparison of matrixassisted laser desorption mass spectrometry is made with high-performance liquid chromatography.     

Assignment of the absolute configuration of blasticidin A and revision of that of aflastatin A

The absolute configuration of blasticidin A, a strong inhibitor of aflatoxin production by Aspergillus parasiticus, was assigned by adding the data of relative configurations at its diol and pentaol moieties to previously known stereochemistry. Similarity of the NMR data of blasticidin A to those of aflastatin A allowed us to revise the stereochemistry of the diol and pentaol moieties of aflastatin A.     

取代芳烃对某些生物急性毒性的拓扑学研究

提出了成键原子的生物活性值(ai),并建立其连接性指数(mA).其中的0A、1A与取代芳烃对斜生栅列藻、日本长腿蛙蝌蚪、绿藻等三种生物的急性毒性关连,相关系数(R)依次为0.9516、0.9564、0.9335,优于相应文献的研究成果.证明mA与取代芳烃生物活性的相关性优于著名的Kier指数(mXv).     

Synthesis of a Mn6 cluster and its self-assembly of an azido-bridged polymer

A rare micro6-oxo-centered Mn6 mixed-valent cluster (1) is prepared and used as a secondary building unit for the self-assembly of its azido-bridged polymeric analogue (2) in a systematic way with the retention of the Mn6 core of 1. Both complexes are characterized by X-ray single-crystal structure determination. The complex 1 was crystallized in a monoclinic system, space group P21, a=11.252(5) A, b=20.893(9) A, c=12.301(6) A, and beta=115.853(7) degrees, whereas the polymeric analogue 2 was crystallized in an orthorhombic system, space group P212121, a=13.1941(8) A, b=14.9897(9) A, and c=27.8746(14) A. Variable-temperature magnetic behavior showed the presence of strong antiferromagnetic interaction in both cases.     

Extent of formation of a dimeric adenine photoproduct in polynucleotides and DNA

Quantum yields are reported for the formation of a dimeric adenine photoproduct, A = A, in adenine homopolymers and DNA irradiated at 254 nm. The A = A content of irradiated samples was assayed by using reversed-phase HPLC to isolate the 4,6-diamino-5-guanidinopyrimidine (DGPY) which is produced from A = A on acid hydrolysis. Acid hydrolysates derived from DNA radiolabelled with [14C] 2'-deoxyadenosine were spiked with unlabelled DGPY before fractionation on HPLC and the recovered material was further purified by chromatography on Sephadex G-10 followed by co-crystallization with DGPY sulphate. Although A = A is formed with a relatively high quantum yield of 1.6 X 10(-3) mol einstein-1 in single-stranded poly(dA) the photoaddition reaction is strongly quenched in base-paired poly(dA).poly(dT) and undetectable in poly(rA).poly(dT). Respective quantum yields of 6 X 10(-5) and 9 X 10(-6) were estimated for the formation of A = A in single- and double-stranded E. coli DNA implying that the photoproduct has very limited biological significance. From studies with d(ApG), d(GpA), ApG, GpA, d(A)20 and d(A4G)4 it is concluded that adjacent guanine and adenine bases do not form a photoadduct analogous to A = A and also that guanine residues have no local or long-range quenching effect on photodimerization within A-A doublets.     

spiro-Mamakone A: a unique relative of the spirobisnaphthalene class of compounds

[structure: see text] A spirobisnaphthalene derivative with a new spiro-nonadiene skeleton, spiro-mamakone A (1), has been isolated from the extract of a cultured nonsporulating fungal endophyte derived from the New Zealand native tree Knightia excelsa (rewarewa). The carbon skeleton of spiro-mamakone A represents a new structural entity and an intriguing addition to the structurally diverse spirobisnaphthalene group of compounds. spiro-Mamakone A is potently cytotoxic and is also antimicrobial.