Two oleananes from Ammannia auriculata Willd

Two new compounds: 3-β,15-α,23,28-tetrahydroxyolean-12-en-3-O-arabinopyaranoside and 3-β,23,28-trihydroxy-olean-12-en-3-O-β-D-glucopyranoside were isolated from the aerial parts of Ammania auriculata along with the known compounds kaempferol, β-sitosterol-3-O-β- D-glucoside, 2-α,3-β,23-trihydroxyolean-12-en-28-oic acid-28-O-β-D-glucopyranoside, quercetin, kaempferol-3-O-α-L-arabinofuranoside, kaempferol-3-O-β-D-xylopyranoside and ellagic acid. Structures of these compounds were elucidated on the basis of their spectroscopic data (NMR, UV, MS and IR spectra). The antioxidant activities of the total extract, the fractions CH(2)Cl(2), EtOAc and the remaining aqueous together with the compounds 1, 6 and 9 were comparable with that of the standard antioxidant, ascorbic acid.     

Towards oleananes: Geminal dimethylation at C-4

A model of the ABC rings of the oleananes, prepared by biomimetic polyene cyclization, shows that the system is sufficiently rigid to prevent epimerization of the C-5 hydrogen with a ketone functionality in place at C-4. Such a sterically hindered ketone has been successfully transformed to a geminal dimethyl group by a three-step procedure.     

seco-C/D ring analogues of ergot alkaloids. Synthesis via intramolecular Heck and ring-closing metathesis reactions

[reaction: see text] Intramolecular Heck and ring-closing metathesis reactions on key intermediates 10 and 15, respectively, provide efficient entries into seco-C/D ring analogues of Ergot alkaloids 12 and 16, compounds of potential synthetic and biological interest.     

Functional biointerface materials inspired from nature

Controlling the interfacial chemical and physical properties, and thus modulating the behaviours of cells and biomolecules on material surfaces, form an important foundation for the development of high-performance biomaterials and devices. Biological systems in nature exhibit unique features in this aspect. The first one is that the superior properties of natural biomaterials are normally not determined by their bulk properties, but more related to the multi-scale micro- and nanostructures on the surface; the second is that biological systems usually utilize highly specific weak interactions (e.g. hydrogen bonding interaction, hydrophobic interaction, etc.) to solve the problems of biomolecule interactions; the third is that the biomolecules in nature are often chiral molecules and show high preference for one specific enantiomorphous configuration, suggesting a distinctive chiral recognition mechanism in biological systems. These features bring much inspiration to design novel biointerface materials with special functionalities, e.g. structural biointerface materials, smart biointerface materials and chiral biointerface materials. The purpose of this critical review is to give a brief introduction of recent advances in these aspects (90 references).     

Protein conformational switches: from nature to design

Protein conformational switches alter their shape upon receiving an input signal, such as ligand binding, chemical modification, or change in environment. The apparent simplicity of this transformation--which can be carried out by a molecule as small as a thousand atoms or so--belies its critical importance to the life of the cell as well as its capacity for engineering by humans. In the realm of molecular switches, proteins are unique because they are capable of performing a variety of biological functions. Switchable proteins are therefore of high interest to the fields of biology, biotechnology, and medicine. These molecules are beginning to be exploited as the core machinery behind a new generation of biosensors, functionally regulated enzymes, and "smart" biomaterials that react to their surroundings. As inspirations for these designs, researchers continue to analyze existing examples of allosteric proteins. Recent years have also witnessed the development of new methodologies for introducing conformational change into proteins that previously had none. Herein we review examples of both natural and engineered protein switches in the context of four basic modes of conformational change: rigid-body domain movement, limited structural rearrangement, global fold switching, and folding-unfolding. Our purpose is to highlight examples that can potentially serve as platforms for the design of custom switches. Accordingly, we focus on inducible conformational changes that are substantial enough to produce a functional response (e.g., in a second protein to which it is fused), yet are relatively simple, structurally well-characterized, and amenable to protein engineering efforts.     

Learning from nature: beta-sheet-mimicking copolymers get organized

The solution structures formed by coil-coil copolymers arise from the selective solvation of one of the two blocks and have been well described. In most cases in such relatively simple synthetic structures there are no specific attractive forces that can aid the aggregation process. Nature, however, provides plenty of inspiring polymeric architectures that are shaped and ordered hierarchically by noncovalent forces. The high level of structural definition displayed by proteins, for example, is unmatched by synthetic polymers. An emerging area of interest in polymer science tries to combine the best of both worlds, the natural and the synthetic, by conjugating synthetic polymers and beta-sheet-forming peptides. Understanding the supramolecular organization of the block copolymers driven exclusively by the intermolecular attractive forces of the peptide sequence is of particular interest. Not only do these peptide-polymer hybrid structures present an interesting new class of materials, they can also provide important insights into self-organization processes prevalent in nature.     

Lessons from nature: biomimetic organocatalytic carbon-carbon bond formations

Nature utilizes simple C2 and C3 building blocks, such as dihydroxyacetone phosphate (DHAP), phosphoenolpyruvate (PEP), and the "active aldehyde" in various enzyme-catalyzed carbon-carbon bond formations to efficiently build up complex organic molecules. In this Perspective, we describe the transition from using enantiopure chemical synthetic equivalents of these building blocks, employing our SAMP/RAMP hydrazone methodology and metalated chiral alpha-amino nitriles, to the asymmetric organocatalytic versions developed in our laboratory. Following this biomimetic strategy, the DHAP equivalent 2,2-dimethyl-1,3-dioxan-5-one (dioxanone) has been used in the proline-catalyzed synthesis of carbohydrates, aminosugars, carbasugars, polyoxamic acid, and various sphingosines. Proline-catalyzed aldol reactions involving a PEP-like equivalent have also allowed for the asymmetric synthesis of ulosonic acid precursors. By mimicking the "active aldehyde" nucleophilic acylations in Nature catalyzed by the thiamine-dependent enzyme, transketolase, enantioselective N-heterocyclic carbene-catalyzed benzoin and Stetter reactions have been developed. Finally, based on Nature's use of domino reactions to convert simple building blocks into complex and highly functionalized molecules, we report on our development of biomimetic asymmetric multicomponent domino reactions which couple enamine and iminium catalysis.     

First natural urease inhibitor from Euphorbia decipiens

Three new diterpene esters with a myrsinol-type skeleton have been isolated from Euphorbia decipiens BOISS. & BUHSE. The structure elucidation of the isolated compounds was based primarily on two-dimensional (2D)-NMR techniques including correlation spectroscopy (COSY), heteronuclear multiple quantum coherence (HMQC), heteronuclear multiple bond correlation (HMBC) and nuclear Overhauser effect spectroscopy (NOESY) experiments. Compounds 1 and 3 are active against prolyl endopeptidase and compound 2 showed inhibitory activity against urease enzyme.     

Profiting from nature: macroporous copper with superior mechanical properties

Macroporous copper with a complex hyperbolic morphology and superior mechanical properties was produced by replicating the remarkable form of a sea urchin skeletal plate using templated electrochemical deposition.     

It from bit: AI and the laws of nature

The present rate of growth of powerful AI systems motivates an accurate comparison between the notion of computers and the workings of natural sciences. Statements such as “intelligence doesn't require flesh, blood or carbon atoms” or “it's computation all the way down” incite a substrate-independent view, providing shortcuts for Darwinian evolution and the possible appearance of sentient machines. This view is discussed and contrasted from a quantum chemical perspective. The qualitative difference between the developed AI and the evolved HI is recognized and the importance of a material constituent, formulated in terms of energy-temperature, conjugate to an immaterial ingredient, in the context of time-entropy, is pointed out as a necessary feature. The popular dictum “it from bit” does not appear valid unless amended with its obverse “bit from it.”     

First synthesis of 1,9-dideoxyforskolin from ptychantin A

1,9-Dideoxyforskolin 2 has been synthesized starting from ptychantin A 3.     

The First Direct Synthesis of Corroles from Pyrrole

The solvent-free, catalyst-free condensation of pyrrole and aldehydes provides an extremely facile synthetic pathway to novel corroles [Eq. (1); Ar=C₆F₅, 2,6-F₂C₆H₃, 2,6-Cl₂C₆H₃]. The product containing pentafluorophenyl groups is an excellent precursor of other derivatives, including an ionic, water-soluble corrole.     

First Representatives of Stable Phosphoranes Derived from Bicyclophosphorylated Carbohydrates

1,2-O-Isopropylidene--D-glucofuranose 3,5,6-phosphite was stidied in reactions with -dicarbonyl compounds. Reagents with the electron-acceptor halogen atom form with the former stable phosphoranes, while unsubstituted -dicarbonyl compounds, the corresponding normal phosphates.     

The First Synthesis of a Diynone from Echinacea pallida

In order to provide an authentic standard and to generate pure material for biological testing, an efficient synthetic route to 1 was developed. This represents the first total synthesis of a major bioactive diynone from E. pallida.     

Rhopeptin A: First Cyclopeptide Isolated from Rhodobryum giganteum

Rhopeptin A was isolated as the first cyclopentapeptide from the moss Rhodobyum giganteum [Schwaegr.] Par . This novel compound consists of proline, phenylalanine, and 3‐hydroxyproline ring‐bonded amino acid residues connected to a tyrosine fragment via an ether bridge. Attached to a 3‐hydroxyproline unit is a side chain of pyroglutamic acid residue. The structure of the peptide was deduced from the 1D‐ and 2D‐NMR and MS data.