pH-regulated formation of amyloid-like beta-sheet assemblies from polyglutamate grafted polyallylamine

A novel artificial protein with simple primary structure, poly(gamma-methyl-L-glutamate)-grafted polyallylamine, has been prepared and the resultant peptide has shown a unique property of pH-regulated conformation and morphology.     

Efficient synthesis of isoplagiochin D, a macrocyclic bis(bibenzyls), by utilizing an intramolecular Suzuki-Miyaura reaction

Isoplagiochin D, a highly strained macrocyclic bis(bibenzyls) with two biaryl units isolated from the liverwort Pladiochila fruticosa, was prepared in 10.6% overall yield for the 11 steps by an efficient synthetic approach involving the construction of two bibenzyl and one biaryl units using Horner-Wadsworth-Emmons and Suzuki-Miyaura protocols.     

Effects of dipole moment, linkers, and chromophores at side chains on long-range electron transfer through helical peptides

Octadecapeptides carrying a ferrocene moiety at the molecular terminal were self-assembled on gold, and long-range electron transfer from the ferrocene moiety to gold was investigated by electrochemical methods. Effects on electron transfer of dipole moment of helical peptides, linkers connecting the peptide to gold, and chromophores introduced into the side chains were discussed. Cyclic voltammetry of the monolayers in an aqueous solution revealed that long-range electron transfer over 40 A occurred along the peptide molecule. Chronoamperometry showed that the long-range electron transfer should be ascribed to a hopping mechanism with use of amide groups as hopping sites. Electron transfer through the long peptide was not significantly accelerated by the dipole moment. However, the linker remarkably affected electron transfer depending on whether it was a methylene chain or a phenylene group, suggesting that local electron transfer between gold and the peptides should be the slowest step to determine the overall rate. Pyrenyl groups introduced into the side chains in the middle of the peptide molecule did not noticeably change electron transfer, probably because pyrenyl groups were too distant to allow direct electron transfer between them. Electrostatic potential profiles across the peptide monolayers were also calculated to explain reasonably the several interesting features in the present peptide systems.     

Studies on the synthesis of compounds related to adenosine 3',5'-cyclic phosphate. IX. Synthesis and cytotoxic effect of adenosine 3',5'-cyclic alkylphosphoramidates.

A series of adenosine 3',5'-cyclic monophosphoramidates (3, cAMP amidates), including long-chain alkyl amidates, were synthesized from adenosine 3',5'-cyclic monophosphate (1, cAMP) by means of a one-pot reaction. This reaction proceeded by the treatment of cAMP tributylammonium salt (2) with phosphorus pentachloride (PCl5) and alkylamine in N,N-dimethylformamide (DMF). Compounds 3 synthesized were investigated to determine their cytotoxic activities on the growth of mouse mastocytoma P-815 cells, mouse mammary tumor FM3A cells, and human mammary tumor ZR-75 cells in culture. It was found that compounds 3h-m showed significant cytotoxic activities against these cell lines, and that cAMP decylamidate (3j) was the most cytotoxic compound (the concentration required for 50% inhibition of cell growth, ID50 = 6.0, 15.0, 2.2 microM, respectively); the antitumor effect on P-815 cells by a total packed cell volume method showed 81.8% inhibition. The cytotoxic activity of 3 increased with the increase in alkyl chain length up to 10 carbon atoms and decreased in compounds having longer alkyl chain.     

Ring transformation of 6H-cyclopropa[e]pyrazolo[1,5-a]pyrimidine. IV (1). Reduction and reaction of 5a-acetyl-6a-ethoxycarbonyl-5a,6a-dihydro-6H-cyclopropa[e]pyrazolo[1,5-a]pyrimidine-3-carbonitriles with primary amines

The reaction of 5a-acetyl-6-ethoxycarbonyl-5a,6a-dihydro-6H-cyclopropa[e]pyrazolo[1,5-a]pyrimidine-3-carbonitrile ( 1a ) with benzylamine gave ethyl l-benzyl-5-cyano-8a,9-dihydro-2-methyl-1H-pyrrolo[3,4-e]-pyrazolo[1,5-a]pyrimidine-8a-carboxylate ( 2a ), in addition to 5-acetyl-3-benzylamino-1-(4-cyanopyrazol-3-yl)- 2-pyridone ( 3 ). Reaction of 1a with aniline gave ethyl 6-acetyl-8-anilino-3-cyano-7,8-dihydro-4H-pyrazolo-[1,5-a][1,3]diazepine-8-carboxylate ( 4 ), in addition to ethyl 3-cyano-7-methyl-6-pyrazolo[1,5-a]pyrimidine-acrylate ( 5 ). On the other hand, the same reactions of 1b with benzylamine or aniline gave 2b or 8b , respectively. Though catalytic hydrogenation of 1a over 5% palladium-carbon proceeded by ring fission of cyclopropane ring to give 9 , 1a (or 1b ) afforded 4,5-dihydro derivatives ( 13 or 15 ) by catalytic hydrogenation over platinum oxide. The reactivity of 5-methoxy-4,5,5a,6a-tetrahydro-6H-cyclopropa[e]pyrazolo[1,5-a]pyrimidine ( 16 ), which are related analogs of 1a,b , is also described.     

2,2′-Isopropylidenebis[(4S,5R)-4,5-di(2-naphthyl)-2-oxazoline] ligand for asymmetric cyclization-carbonylation of meso-2-alkyl-2-propargylcyclohexane-1,3-diols

The oxidative cyclization-carbonylation of meso-2-alkyl-2-propargylcyclohexane-1,3-diols mediated by Pd(II) with chiral bisoxazoline (box ligand) afforded bicyclic-β-alkoxyacrylates. Based on a ligand screening, 2,2′-isopropylidenebis[(4S,5R)-4,5-di(2-naphthyl)-2-oxazoline] ligand has been developed. The products with a chiral quaternary carbon were obtained in 71-100% yields with 85-95% ee.     

Synthetic studies directed toward the assembly of the C-glycoside fragment of the telomerase inhibitor D8646-2-6

[reaction: see text] Construction and characterization of the C-glycosidic moiety of telomerase inhibitor D8646-2-6 (1) are described. This is the first example of the C-glycosylation using electron-poor aromatics, 4-hydroxypyrone, as a glycosyl acceptor. The glycosylation reaction and base-promoted isomerization affords desired beta-C-glycoside in a 61% overall yield.     

The first synthesis of a methano[60]fullerene with an electron-donating group at the methano-bridge carbon: synthesis and reaction of aminomethano[60]fullerene

[reaction: see text] Aminomethano[60]fullerene was synthesized for the first time as a trifluoromethanesulfonic acid salt by applying the Curtius rearrangement of azidocarbonylmethano[60]fullerene as the key reaction. Aminomethano[60]fullerene thus obtained was found to be able to react with various acyl chlorides to afford the corresponding amides.     

Structure and ethanol complexation of cyclic tetrasaccharide in aqueous solution studied by NMR and molecular mechanics

The structure and ethanol complexation of a cyclic tetrasaccharide (CTS) in aqueous solution were investigated by proton NMR spectroscopy and molecular mechanics calculations. Two glucose units, A and B, of CTS are alternatively bonded by alpha-1,3 and alpha-1,6 linkages. The overlapped signals of protons A5, A6S, A6R, B3, B6S and B6R were resolved by spectral simulations to determine their chemical shifts and vicinal coupling constants. All vicinal coupling constants except for the A5-A6 spin system are consistent with the dihedral angles in the X-ray crystal structure. Each of protons A5, A6S, and A6R in the two units of A is equivalent with respect to the chemical shift. The vicinal coupling constants of (3)J(5-6S) and (3)J(5-6R) for unit A are close to the average of two rotamers that are present in crystals. The intensities of cross-peaks in the rotating frame nuclear Overhauser effect spectroscopy (ROESY) spectrum were rather well correlated with the effective distances calculated for the X-ray structure and molecular mechanics structures calculated in vacuo and water, although they are slightly better correlated with molecular mechanics structure in vacuo than with the other structures. From the changes of the chemical shifts of several CTS protons with increasing ethanol concentration, it was suggested that adsorption sites of ethanol on the plate structure of CTS are protons B2 and B4 (site B) in the concave face side and protons A1 and A2 (site A) in the convex back side. The binding constants for sites A and B are 0.0061 and 0.0176 M(-1), respectively. These binding constants are much smaller than a value of 4.1 M(-1) for the ethanol-alpha-cyclodextrin complex.     

Ring‐Opening Reactions of 3‐Aryl‐1‐benzylaziridine‐2‐carboxylates and Application to the Asymmetric Synthesis of an Amphetamine‐Type Compound

Nucleophilic ring‐opening reactions of 3‐aryl‐1‐benzylaziridine‐2‐carboxylates were examined by using O‐nucleophiles and aromatic C‐nucleophiles. The stereospecificity was found to depend on substrates and conditions used. Configuration inversion at C(3) was observed with O‐nucleophiles as a major reaction path in the ring‐opening reactions of aziridines carrying an electron‐poor aromatic moiety, whereas mixtures containing preferentially the syn‐diastereoisomer were generally obtained when electron‐rich aziridines were used (Tables 1–3). In the reactions of electron‐rich aziridines with C‐nucleophiles, S_N2 reactions yielding anti‐type products were observed (Table 4). Reductive ring‐opening reaction by catalytic hydrogenation of (+)‐trans‐(2S,3R)‐3‐(1,3‐benzodioxol‐5‐yl)aziridine‐2‐carboxylate (+)‐trans‐ 3c afforded the corresponding α‐amino acid derivative, which was smoothly transformed into (+)‐tert‐butyl [(1R)‐2‐(1,3‐benzodioxol‐5‐yl)‐1‐methylethyl]carbamate((+)‐ 14 ) with high retention of optical purity (Scheme 6).