Syntheses of helical polymers through the combination of axially dissymmetric segments

Wholly aromatic polymers with various helical structures were prepared through the combination of two axially dissymmetric bifunctional compounds. The palladium-catalyzed condensation of (R)-2,2-diethoxy-6,6′-dibromo-1,1′-binaphthyl with (R)-1,1′-binaphthyl-2,2′-diamine and the reaction of (S)-2,2-diethoxy-6,6′-dibromo-1,1′-binaphthyl with (S)-1,1′-binaphthyl-2,2′-diamine produced helical polyamines, and the chiral conformation was confirmed by their circular dichroism spectra and large specific rotations. The combination of (R)-2,2-diethoxy-6,6′-dibromo-1,1′-binaphthyl and (S)-1,1′-binaphthyl-2,2′-diamine afforded polyamines with a zigzag conformation. The condensation of (R)-2,2′-dimethylbiphenyl-6,6′-dicarbonyl chloride with (R)-2,2′-diamino-6,6′-dimethylbiphenyl and the reaction of (S)-2,2′-dimethylbiphenyl-6,6′-dicarbonyl chloride with (S)-2,2′-diamino-6,6′-dimethylbiphenyl predominantly yielded cyclic dimers and tetramers because of the steric proximity of the reactive groups of the propagating species. The experimental results indicated that the structures of the obtained polymers depended on the combination of the chirality of the bifunctional atropisomeric compounds and the position of the functional groups on the aromatic rings. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4607–4620, 2004     

Electrospray mass spectrometry of pentacosasaccharides of blood group I-activity and related compounds

The structural characterization of large synthetic oligosaccharides and related glycoconjugates performed by the use of electrospray ionization mass spectrometry (ESIMS) is described. The largest molecules described here are unprotected and protected pentaantennary pentacosasaccharides 2 and 5 with average molecular masses of 4441 and 9416, respectively. The straight-chain neutral ceramide decasaccharide (d18:1/c24:0) 6 and the disialoganglioside GD2 (d18:1/c24:0) 7 were also successfully analyzed by ESIMS. In addition to exact mass determination, collision-induced dissociation (CID) spectrometry of these compounds provided saccharide chain sequence information.     

A synthetic approach to seven-membered lactones by the microbial transformation of ynones having a trifluoromethyl group

Studies on the microbial transformations of a number of ynones bearing a trifluoromethyl group prepared by the reaction of ethyl trifluoroacetate with a variety of lithium alkynates, have been undertaken. The major products were the corresponding carbinols but microbial carbon-carbon bond degradation and formation occurred also, which proceeded to novel fluorinated seven-membered lactones as significant products.     

Synthesis of Block Copolymers and Asymmetric Star-Branched Polymers Comprised of Polyacetylene and Polystyrene Segments via Ionic Bond Formation

Novel ion-bonded AB diblock copolymers and three-arm AB₂ asymmetric star-branched polymers comprised of polyacetylene (A) and polystyrene (B) segments have been synthesized by the stoichiometric reaction of tert-amine-chain-end-functionalized poly(phenyl vinyl sulfoxide)s with either chain-end- or in-chain-carboxylated polystyrenes to link the two polymer segments via ionic bond, followed by thermal treatment to convert their poly(phenyl vinyl sulfoxide)s to polyacetylene segments. Periodic lamellar morphologies were observed in the cast films of such polymers by TEM measurement. The isolation of the nano-size sheet consisting of polyacetylene lamellar layers was attempted.     

Preparation and regioselective reactions of novel gem-difluorinated vinyloxiranes with some organometallic reagents

Hitherto unknown, relatively labile gem-difluorinated vinyloxiranes were prepared by difluoro-Wittig reactions with alpha,beta-epoxyketones; for these vinyloxiranes alkyl groups were delivered at the fluorine-attached terminal carbon atom in an SN2' manner by RLi, while Me3Al and MeMgBr-CuCl (3: 1) introduced the Me group at the allylic epoxy carbon with retention and inversion of the original stereochemistry, respectively.     

Stannylative cycloaddition of enynes catalyzed by palladium-iminophosphine

Palladium-iminophosphine complex catalyzes stannylative cycloaddition of conjugated enynes using hexabutyldistannoxane as a stannylating agent to afford highly substituted 3-alkenylphenylstannanes regioselectively. Stannylative cross-cycloaddition reactions between different enynes or between enynes and diynes are also achieved. The reaction is successfully applied to a concise synthesis of alcyopterosin N, which has been isolated recently from sub-Antarctic soft coral, Alcyonium paessleri.     

Contortisiliosides A–G: Isolation of Seven New Triterpene Bisdesmosides from Enterolobium contortisiliquum and Their Cytotoxic Activity

Seven new bisdesmosidic triterpene saponins, with up to eight monosaccharides, which were given the trivial names contortisiliosides A–G ( 1 – 7 ), were isolated from Enterolobium contortisiliquum. The structures of the new saponins were determined on the basis of extensive spectroscopic and chromatographic analyses of both intact and acid‐hydrolyzed compounds. The isolated saponins were evaluated for their cytotoxic activities against BAC1.2F5 mouse macrophages, EL‐4 mouse lymphoma cells, and L‐929 mouse fibroblasts. Whereas contortisiliosides A ( 1 ) and C ( 3 ) were moderately cytotoxic to both BAC1.2F5 macrophages and EL‐4 cells, and contortisiliosides D–G ( 4 – 7 ) did not show any apparent cytotoxic activities against the three cell lines, contortisilioside B ( 2 ) exhibited selective cytotoxic activity against BAC1.2F5 mouse macrophages, with an IC₅₀ value of 3.4 μM . The macrophage death caused by 2 was shown to be neither necrotic nor apoptosis‐inducing based on the unique morphological change of the killed cells, whose cytosols were transformed into large vacuoles, and according to the TUNEL assay.     

Fine tuning of photophysical properties of meso-meso-linked ZnII-diporphyrins by dihedral angle control

A series of meso-meso-linked diporphyrins S(n) strapped with a dioxymethylene group of various length were synthesized by intramolecular Ag(I)-promoted coupling of dioxymethylene-bridged diporphyrins B(n), for n=10, 8, 6, 5, 4, 3, 2, and 1. Shortening of the strap length causes a gradual decrease in the dihedral angle between the porphyrins and increasing distortion of porphyrin ring, as suggested by MM2 calculations and (1)H NMR studies. This trend has been also suggested by X-ray crystallographic studies on the corresponding Cu(II) complexes of nonstrapped diporphyrin 2 Cu, and strapped diporphyrins S(8)Cu, S(4)Cu, and S(2)Cu. The absorption spectrum of relatively unconstrained diporphyrins S(10) strapped with a long chain exhibits split Soret bands at 414 and 447 nm and weak Q(0,0)- and prominent Q(1,0)-bands, both of which are similar to those of nonstrapped diporphyrin 2. Shortening of the strap length causes systematic changes in the absorption spectra, in which the intensities of the split Soret bands decrease, the absorption bands at about 400 nm and > 460 nm increase in intensity, and a prominent one-band feature of a Q-band is changed to a distinct two-band feature with concurrent progressive red-shifts of the lowest Q(0,0)-band. The fluorescence spectra also exhibit systematic changes, roughly reflecting the changes of the absorption spectra. The strapped diporphyrins S(n) are all chiral and have been separated into enantiomers over a chiral column. The CD spectra of the optically active S(n) display two Cotton effects at 430-450 and at about 400 nm with the opposite signs. The latter effect can be explained in terms of oblique arrangement of m( perpendicular 1) and m( perpendicular 2) dipole moments, while the former effect cannot be accounted for within a framework of the excition coupling theory. The resonance Raman (RR) spectra taken for excitation at 457.9 nm are variable among S(n), while the RR spectra taken for excitation at 488.0 nm are constant throughout the S(n) series. These photophysical properties can be explained in terms of INDO/S-SCI calculations, which have revealed charge transfer (CT) transitions accidentally located close in energy to the excitonic Soret transitions. This feature arises from a close proximity of the two porphyrins in meso-meso-linked diporphyrins. In addition to the gradual red-shift of the exciton split Soret band, the calculations predict that the high-energy absorption band at about 400 nm, the lower energy Cotton effect, and the RR spectra taken for excitation at 457.9 nm are due to the CT states which are intensified upon a decrease in the dihedral angle.     

Fabrications of potential imaging probes based on a β-alkyl substituted porphyrin with a terpyridine external coordination site

We report synthesis and coordination properties of β-alkyl porphyrin derivatives bearing terpyridylphenyl substituents at the meso-position and propionate side chains at the β-positions. Rhenium(I) carbonyl ion was encapsulated not in the core but in the external terpyridyl ligand. Such porphyrin-terpyridine hybrid porphyrins can be potentially available for less-invasive imaging like SPECT.