Artificial plant cell walls as multi-catalyst systems for enzymatic cooperative asymmetric catalysis in non-aqueous media.

The assembly of cellulose-based artificial plant cell wall (APCW) structures that contain different types of catalysts is a powerful strategy for the development of cascade reactions. Here we disclose an APCW catalytic system containing a lipase enzyme and nanopalladium particles that transform a racemic amine into the corresponding enantiomerically pure amide in high yield via a dynamic kinetic resolution.

Acetal containing polymers as pH-responsive nano-drug delivery systems.

Utilization of unique acidic environment in various disease sites has been quite advantageous in targeted drug delivery. Among the widely explored pH-sensitive moieties such as hydrazone, orthoester, imine, vinylether, etc., the acetal bearing compounds are one of the most explored entities in targeted and improved drug delivery to treat disease conditions at the preclinical stage. This review addresses the design and synthesis of various acetal-based polymers as pH-responsive nano-drug delivery systems in the form of micelles, polymersomes, nanoplexes and polymeric and solid lipid nanoparticles for biomedical applications. The review will identify potential advantages, key challenges and future prospects of acetal-based pH-responsive drug delivery systems. The novel developments, strategies and suggestions described may guide the formulation scientists to optimize acetal-based pH-responsive drug delivery systems as an approach to treat various diseases.

Synthesis of Cross-Conjugated Polyenes via Palladium-Catalyzed Oxidative C-C Bond Forming Cascade Reactions of Allenes.

An efficient palladium-catalyzed oxidative C-C bond forming cascade reaction of allenes involving a coupling between an enallene and an allenyne followed by a carbocyclization of the generated Pd-intermediate was developed. This cascade reaction afforded functionalized cross-conjugated polyenes. The enallene is initially activated by palladium and reacts with the allenyne to give the cross-conjugated polyenes.

Selective Cascade Reaction of Bisallenes via Palladium-Catalyzed Aerobic Oxidative Carbocyclization-Borylation and Aldehyde Trapping.

A cascade reaction, consisting of a palladium-catalyzed regioselective aerobic oxidative carbocyclization-borylation of bisallenes and a final aldehyde trapping, afforded triene alcohols with high diastereoselectivity. The cascade reaction occurs under mild reaction conditions and proceeds via an allylboron intermediate that is trapped by the aldehyde in a stereoselective manner.

A foldamer-based chiroptical molecular switch that displays complete inversion of the helical sense upon anion binding.

Chiral indolocarbazole dimers fold into a helical conformation by virtue of intramolecular hydrogen bonds, as demonstrated by (1)H NMR and CD spectra and optical rotations. In particular, the optical properties of the dimers were found to be extremely sensitive to the nature of the solvent, depending on whether they are folded or not. The helical sense of the dimers can be reversibly switched by binding sulfate ion, which gives rise to complete inversion of the CD spectra. The binding mode and absolute stereochemistry of the sulfate complexes was unequivocally determined by single-crystal X-ray structures, which are all consistent with the CD and (1)H NMR spectra in solution.

Folding and anion-binding properties of fluorescent oligoindole foldamers.

A series of oligoindole foldamers 1 a-d that are highly fluorescent were prepared by using a biindole derivative as the repeating unit, and their folding and anion-binding properties were revealed by (1)H NMR and fluorescence spectroscopy. The oligoindoles exist in an extended conformation, but adopt a compact helical structure in the presence of an anion. The anion is entrapped inside the tubular cavity of the helical strand, comprising four aryl units per turn, by multiple hydrogen bonds with the indole NHs. These structural features were confirmed by (1)H NMR and fluorescence spectroscopy. When folded by anion binding, 1 b-d show characteristic downfield shifts of the NH signals and upfield shifts of the aromatic CH signals by Deltadelta=0.1-1.0 ppm. The average chemical shift for all the aromatic signals of 1 a-d is more upfield shifted as the chain lengthens, as anticipated from the degree of overlapped aromatic surfaces in the helical strand. Moreover, 1 a-d are strongly fluorescent in the absence of an anion. Upon binding an anion such as a chloride, the shorter oligoindoles 1 a and b lead to negligible change in the emission spectra, whereas the longer ones 1 c and d result in dramatic changes, that is, large hypochromic and bathochromic shifts (Deltalambda=65 and 70 nm) of the emission band, confirming the helical folding. The association constants (K(a)) between oligoindoles and tetrabutylammonium chloride strongly depend on the chain length; <1 M(-1) for 1 a, 630 M(-1) for 1 b, 1.1x10(5) M(-1) for 1 c, and 2.9x10(5) M(-1) for 1 d in 20 % (v/v) MeOH/CH(2)Cl(2) at 24+/-1 degrees C. In addition, the association constants of 1 c and 1 d with other anions such as fluoride, bromide, iodide, azide, cyanide, acetate, and nitrate are determined to be in the order of 10(3)-10(6) M(-1) under the same conditions.

Biased helical folding of chiral oligoindole foldamers.

Oligoindole-based chiral foldamers have been synthesized by incorporating (S)- or (R)-1-phenylethylamine to both ends of the tetraindole scaffold. The oligoindoles fold into a helical conformation upon binding an anion by hydrogen bonds, which gives rise to an induced circular dichroism (CD) signal of large amplitude, implying the preferential formation of one helical isomer over another. Theoretical calculations suggest that the (P)-helix of the (S,S)-oligoindole 8a be more energetically stable than the corresponding (M)-helix.