Total synthesis of azumamide A and azumamide E, evaluation as histone deacetylase inhibitors, and design of a more potent analogue

The unprecedented diastereoselective Mannich reaction of a Z-allylsulfoximine was a key step in the total synthesis of the marine natural products azumamide A and E, and an unnatural analogue. Their relative potency as histone deacetylase inhibitors was evaluated and found to correlate with predicted zinc-binding affinity. [reaction: see text]     

The structures of three new shishididemniols from a tunicate of the family Didemnidae

Three new serinolipid derivatives, shishididemniols C (1), D (2), and E (3), were isolated as antibacterial constituents of a tunicate of the family Didemnidae. Their planar structures were elucidated by interpretation of NMR and MS data, whereas the absolute stereochemistry was determined by chemical conversions. Shishididemniols C (3), D (4), and E (5) exhibited antibacterial activity against the fish pathogenic bacterium Vibrio anguillarum.     

Comparative study of the water oxidizing reactions and the millisecond delayed chlorophyll fluorescence in photosystem II at different pH

Water splitting activity, the multiline EPR signal associated with S(2)-state of the CaMn(4)-cluster and the fast and slow phases of the induction curve of the millisecond delayed chlorophyll fluorescence from photosystem II (PSII) in the pH range of 4.5-8.5 were studied in the thylakoid membranes and purified PSII particles. It has been found that O(2) evolution and the multiline EPR signal were inhibited at acidic (pK approximately 5.3) and alkaline (pK approximately 8.1) pH values, and were maximal at pH 6.0-7.0. Our results indicate that the loss of O(2) evolution and the S(2)-state multiline EPR signal associated with the decrease of the millisecond delayed chlorophyll fluorescence only in alkaline region (pH 7.0-8.5). Possible correlations of the millisecond delayed chlorophyll fluorescence components with the donor side reactions in PSII are discussed.     

External electric field effects on absorption, fluorescence, and phosphorescence spectra of diphenylpolyynes in a polymer film

External electric field effects on absorption, fluorescence, and phosphorescence spectra of a series of unsubstituted diphenylpolyynes have been examined in a PMMA film. The analysis of the electroabsorption spectra indicates that the shorter diphenylpolyynes exhibit only the change in molecular polarizability, whereas the longer ones exhibit the change both in dipole moment and in molecular polarizability following absorption. The finding of the change in dipole moment following absorption of centrosymmetric diphenylpolyynes is interpreted in terms of the symmetry distortion upon doping a polymer film. When the external electric field is applied, the fluorescence yield is reduced and enhanced, respectively, in diphenylacetylene and diphenyloctatetrayne, indicating that the rate of the nonradiative process from the fluorescence state is accelerated in diphenylacetylene and decelerated in diphenyloctatetrayne by an external electric field. All of the diphenylpolyynes used in the present study exhibit the change in molecular polarizability following the phosphorescence process.     

Series of trinuclear NiIILnIIINiII complexes derived from 2,6-Di(acetoacetyl)pyridine: synthesis, structure, and magnetism

Eighteen trinuclear NiII2LnIII complexes of 2,6-di(acetoacetyl)pyridine (H2L) (Ln=La-Lu except for Pm) were prepared by a "one-pot reaction" of H2L, Ni(NO3)2.6H2O, and Ln(NO3)3.nH2O in methanol. X-ray crystallographic studies indicate that two L2- ligands sandwich two NiII ions with the terminal 1,3-diketonate sites and one LnIII ion with the central 2,6-diacylpyridine site, forming the trinuclear [Ni2Ln(L)2] core of a linear NiLnNi structure. The terminal Ni assumes a six-coordinate geometry together with methanol or water molecules, and the central Ln assumes a 10-coordinate geometry together with two or three nitrate ions. The [Ni2Ln(L)2] core is essentially coplanar for large Ln ions (La, Ce, Pr, Nd) but shows a distortion with respect to the two L2- ligands for smaller Ln ions. Magnetic studies for the Ni2Ln complexes of diamagnetic LaIII and LuIII indicate an antiferromagnetic interaction between the terminal NiII ions. A magnetic analysis of the Ni2Gd complex based on the isotropic Heisenberg model indicates a ferromagnetic interaction between the adjacent NiII and GdIII ions and an antiferromagnetic interaction between the terminal NiII ions. The magnetic properties of other Ni2Ln complexes were studied on the basis of a numerical approach with the Ni2La complex and analogous Zn2Ln complexes, and they indicated that the NiII-LnIII interaction is weakly antiferromagnetic for Ln=Ce, Pr, and Nd and ferromagnetic for Ln=Gd, Tb, Dy, Ho, and Er.     

Lipase-catalyzed asymmetric synthesis of desprenyl-carquinostatin A and descycloavandulyl-lavanduquinocin

An asymmetric synthesis of the core carbazole structure, 6-desprenyl-carquinostatin 3 and 6-descycloavandulyl-lavanduquinocin 3, toward a total synthesis of carquinostatin A (1) and lavanduquinocin (2), has been established. Lipase QLM (Meito) catalyzed enantioselective acetylation of the racemic alcohol 6 gave the (-)-acetate 7 and the (+)-alcohol 6 with high enantioselectivity. The absolute stereochemistry of the (-)- and (+)-alcohol 6 have been determined to be R- and S-configurations, respectively, by the advanced Mosher method. In the same manner, the (-)-acetate 13 and the (+)-alcohol 12 have been obtained from the racemic alcohol 12. The (R)-(-)-acetate 13, derived from the (R)-(-)-acetate 7, was the same as the (-)-acetate 13, which has been determined to be (R)-configuration. Oxidation of the (R)-(-)-acetate 13 followed by hydrolysis afforded (R)-(-)-6-desprenyl-carquinostatin [and (R)-(-)-6-descycloavandulyl-lavanduquinocin] 3. In addition, oxidation of the (S)-(+)-alcohol 12 provided (S)-(+)-3, which is the enantiomer of 6-desprenyl-carquinostatin A (R)-(-)-3.     

N-long-chain monoacylated derivatives of 2,6-diaminopyridine with antiviral activity

N-Monoacyl-2,6-diaminopyridines (2a-c) and N,N'-diacyl-2,6-diaminopyridines (3a-c) were synthesized from 2,6-diaminopyridine by acylation with the corresponding acyl halide or by dehydration with the corresponding carboxylic acid using 1,3-dicyclohexylcarbodiimide (DCC). The antiviral activities of N-monoacyl- and N,N'-diacyl-2,6-diaminopyridines (2a-c and 3a-c) were estimated using plaque reduction assay with HSV-1. All N-monoacyl derivatives (2a-c) showed significant anti-herpes simplex virus (HSV)-1 activity (EC(50) = 15.3-18.5 microg/ml). The CC(50) values of 2a-c measured using Vero cells ranged at 37.5-50.0 microg/ml. These compounds showed no significant antibacterial activities with Escherichia coli or Staphylococcus aureus even at a concentration of 1 mg/ml. The N,N'-diacyl derivatives (3a-c) showed no significant anti-HSV-1 activity.     

Linearly polarized ultraviolet photoreaction of photocrosslinkable polymers comprising the p-phenylenediacrylate group and photoalignment control of liquid crystals on the resultant film

We present (1) the linearly polarized (LP) ultraviolet (UV) photoreaction of block copolyesterethers comprising a hard segment of polyester and soft segment of poly(tetramethylene ether) (PTMG) and (2) the alignment behavior of liquid crystals (LCs) on the resultant photoreacted polymer films. Two kinds of copolyesterethers with different polyester segments of poly(hexamethylene p-phenylenediacrylate) (1a) or poly(hexamethylene p-phenylenediacrylate)-co-poly(hexamethylene 1,4-dibenzoate) (1b) were used in this study. The LP–UV irradiation resulted in a negative optical anisotropy for both polymer films, and a homogeneous photoalignment of LCs was achieved on the photoreacted polymer film. The LC alignment was perpendicular to the electric vector of the incident polarized light for 1a, whereas a reversion of the alignment from parallel to perpendicular was observed for 1b, depending on the irradiation doses. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 4000–4006, 1999     

Oligo(ethylene glycol)/alkyl‐modified Chromophore Assemblies for Photon Upconversion in Water

Molecular self‐assembly is a powerful means to construct nanoscale materials with advanced photophysical properties. Although the protection of the photo‐excited states from oxygen quenching is a critical issue, it still has been in an early phase of development. In this work, we demonstrate that a simple and typical molecular design for aqueous supramolecular assembly, modification of the chromophoric unit with hydrophilic oligo(ethylene glycol) chains and hydrophobic alkyl chains, is effective to avoid oxygen quenching of triplet–triplet annihilation‐based photon upconversion (TTA‐UC). While a TTA‐UC emission is completely quenched when the donor and acceptor are molecularly dispersed in chloroform, their aqueous co‐assemblies exhibit a clear upconverted emission in air‐saturated water even under extremely low chromophore concentrations down to 40 μm . The generalization of this nano‐encapsulation approach offers new functions and applications using oxygen‐sensitive species for supramolecular chemistry.