Electron transfer between intercalators bound to DNA are remarkably efficient and point to the double helix as a unique matrix which facilitates chemistry from a distance. When the stacked DNA bases not only mediate electron transfer but also serve as reactants, selective oxidative damage at guanine bases (see below) and repair of lesions in thymine dimers may be promoted from a remote site.

Selectivities that begin to rival those obtained by traditional enzymatic methods are achieved in some recently developed nonenzymatic techniques for the kinetic resolution of secondary alcohols (see scheme below). The most promising approaches are surveyed.

The first total synthesis of a spongipyran macrolide, altohyrtin C (spongistatin 2; see picture below), has been realized. The spongipyrans derived from marine sponges are among the most potent cytotoxic compounds yet isolated, and exhibit subnanomolar activities against a variety of human cancer cell lines. While the structures proposed for the independently isolated altohyrtins and spongistatins are largely homologous, they differ significantly with regard to internal stereochemical relationships. This discrepancy has been resolved by the total synthesis, which verifies the altohyrtin structural assignment and establishes the identity of altohyrtin C and the independently isolated spongistatin 2.

The first total synthesis of a spongipyran macrolide, altohyrtin C (spongistatin 2; see picture below), has been realized. The spongipyrans derived from marine sponges are among the most potent cytotoxic compounds yet isolated, and exhibit subnanomolar activities against a variety of human cancer cell lines. While the structures proposed for the independently isolated altohyrtins and spongistatins are largely homologous, they differ significantly with regard to internal stereochemical relationships. This discrepancy has been resolved by the total synthesis, which verifies the altohyrtin structural assignment and establishes the identity of altohyrtin C and the independently isolated spongistatin 2.

The first total synthesis of a spongipyran macrolide, altohyrtin C (spongistatin 2; see picture below), has been realized. The spongipyrans derived from marine sponges are among the most potent cytotoxic compounds yet isolated, and exhibit subnanomolar activities against a variety of human cancer cell lines. While the structures proposed for the independently isolated altohyrtins and spongistatins are largely homologous, they differ significantly with regard to internal stereochemical relationships. This discrepancy has been resolved by the total synthesis, which verifies the altohyrtin structural assignment and establishes the identity of altohyrtin C and the independently isolated spongistatin 2.

Intercalation and sequence selectivity characterize the binding of the anthraquinone–carbohydrate hydrid 1 to DNA. Important for this binding and for the cytotoxicity of 1 is the hybrid structure, which is based on that of several natural antitumor antibiotics. The enantiomer of 1 is about six times less cytotoxic because of its distinctly reduced intercalation potential.

Deconjugated esters 1 and AD mix α or AD mix β give cis-configured γ-alkyl-β-hydroxy-γ-lactones 2. They are versatile precursors for γ-chiral butenolides and γ-chiral butyrolactones of moderate to high enantiomeric purity, as shown through their conversion into the natural products 3 (92% ee), 4 (95% ee), 5 (97% ee), and 6 (78% ee).

The new ligand hexakis(imidazol-1-ylmethyl)benzene (hkimb, 1) forms a heavily hydrated coordination polymer with CdF₂ of composition Cd(hkimb)F₂ · 14 H₂O. A unique aspect of the structure is that the water assembles itself into two independent and different hydrogen-bonded 2D networks, which interweave throughout the 3D α-Po-related coordination polymer network.

Fused parallelogrammic rings sharing all sides are seen in the structure of 1 (shown below). This atomic cloth was prepared by photopolymerizing alkatetryne molecules that were vapor-deposited and laid flat on graphite. The structural fit between the atomic cloth and the substrate, observed by scanning tunneling microscopy, enables one to determine the unit mesh.

A ten-membered heterometallic ring complex with a T-shaped CuHgFe₂ framework is the result of a bonding CuHg interaction (CuHg 2.668(6) Å). In solution this complex exhibits a motion comparable to a “molecular torsion pendulum” (shown schematically below), which generates an average mirror plane containing the four metal atoms; in the solid state only a C₂ axis is present.

By tuning the donor–acceptor strength in heterocyclic methine dyes such as 1, the cyanine limit was accessible. Despite almost vanishing second-order polarizabilities (β) this new class of chromophores sets a new hallmark for photorefractive applications. With a dye content of only 20% complete diffraction of the readout beam is achieved at a wave-length of 790 nm and a field strength of 68 V μm⁻¹.

“Smart” self-assembly of several chiral diols and an achiral pre-catalyst results in the formation of a highly enantioselective catalyst for the carbonyl–ene reaction (a). The assembly is not influenced by the order of addition of the components and always results in the exclusive formation of a single catalyst, as shown by NMR spectroscopy studies.

The type of intramolecular stabilization of zirconium borate betaines is governed by the location of the substituents in the allyl unit: E configuration results in ZrF coordination (1), whereas Z configuration favors the formation of an internal ZrCH2[B] ion pair (2).

D_3d symmetry characterizes complex 1 (see structure on the right). This circular molecular contains 18 high-spin, antiferromagnetically coupled iron(III) centers. Isolated as the double salt 1 · 6Et₄N(NO₃) · 15CH₃OH · 6Et₂O · 24H₂O it is the largest cyclic ferric cluster yet reported.

C-1′H and not C-2′H is the initial site of oxidative cleavage of DNA with the chemical nuclease [Cu(phen)₂]⁺/H₂O₂. This is the result of experiments with DNA containing C-1′-deuterated thymidine groups (the first step of the reaction sequence is shown below). If C-2′H is extracted in the first step, a one-electron oxidation and H/D migration should take place; there is no evidence of this.

A markedly different emission behavior is exhibited by the two rhenium complexes 1 and 2. These can be interconverted photochemically; the forward reaction (cyclization to the “closed” form) is triggered by visible light, and the reverse reaction by UV light. Therefore, this is a photoswitchable molecular system in which the anthracene groups function as the switching unit and the complexed rhenium as the detector.

Forty-five cationic sites are present in the dendrimer shown schematically on the right, which was obtained by an efficient convergent synthesis. The key step in the reaction sequence for generation growth is the high-yielding Menschutkin reaction

Configurationally stable even at 0°C, the lithiated benzyl thiocarbamate (S)-1 can be substituted by most electrophilic reagents with inversion of configuration. It is the first enantiomerically pure α-thiocarbanion whose outstanding configurational stability allows synthetic use.

The highest known binding constant for the silver(I) complex with a cyclen-derived ligand was recently measured (lg K = 19.63; crystal structure shown on the right). This ligand is preorganized in the metal-free form. It contains four nitrogen and four sulfur atoms, but the soft silver(I) ion prefers coordination through the nitrogen atoms and binds to only two sulfur atoms in the solid state. The chelating ligand was designed for in vivo therapeutic application of the β-emitting radio-nuclide ^IIIAg.

Alternating physisorption and chemical activation characterizes the method presented here for assembling thin, defined organic multilayers (shown schematically on the right). A variety of structures are suitable for the new process, with which even noncentrosymmetric films can be obtained.

Trigonal prismatic at pH 4, octahedral at pH 6.5! A simple change of pH reversibly switches the coordination geometry of a macrocyclic dicobalt(II) complex. The structural change is induced by bridging of the metal ions by a hydroxide ion (see below).

Loss of the carbohydrate structure accompanies the sigmatropic rearrangement of the doubly unsaturated saccharide derivative 1. In this way, a highly functionalized eight-membered carbocycle (2) is obtained in a simple reaction sequence from D-glucose.

With a 5′-GPu-3′ sequence selectivity that is very similar to that of the natural antitumor antibiotic kapurimycin A₃ (1), the ABC ring analogue 2 effectively cleaves DNA by guanine alkylation. Essential for cleavage activity are the reactive alkenyl epoxide group in the side chain and the strong intercalation of the aromatic units of 1 and 2 in the DNA duplex; this was made clear by the significantly lower activity of an AB ring analogue.

Clusters with and without cavities are formed in the reaction of [CdCl₂(PPh₃)₂] with PhSeSiMe₃. Depending on the organic solvent used, [Cd₁₀Se₄(SePh)₁₂(PPh₃)₄] or [Cd₁₆(SePh)₃₂(PPh₃)₂] (depicted on the right; the cluster is almost completely covered with phenyl rings) crystallizes. The clusters are composed of fused adamantanoid CdSe cages.

Two economical and practical sets of conditions have been developed for the Pauson–Khand reaction on the basis that primary amines accelerate this reaction. One method employs more than three equivalents of cyclohexylamine in 1,2-dichloroethane at 83°C, whereas the other requires a mixed solvent of 1,4-dioxane and 2 m aqueous NH₃ (1/3 v/v) at 100°C. Under these conditions, for instance, the cylization shown below is complete in 5 or 15 minutes, respectively, and the product is isolated in 99 or 93% yield, respectively.

Up to 80% yields of cyclotrimers, including 2 depicted below, can be achieved by reaction of bromo(stannyl)alkenes such as 1 with Cu(NO₃)₂ · 3H₂O at room temperature in THF. This route, a definite improvement over previously reported methods, makes such molecules available in sufficient quantity for study, for example, as precursors of fullerene fragments.

Strongly compressed Si-O-N angles are observed in H₃SiONMe₂ (crystal structure shown on the right) and H₂Si(ONMe₂)₂ with respect to the Si-O-C angle in isoelectronic SiOC compounds. This is due to weak donor–acceptor bonds between the Si and N atoms. The resulting partial hypercoordination at silicon explains the unique chemical behavior of hydroxylaminosilanes.

A winning combination! PHONA – PNA co-oligomers such as 1 (T = 1-thyminyl) unite the outstanding binding properties of PNAs with the improved physical properties of PHONAs—in particular, their excellent water solubility.

A two-dimensional labyrinth is formed by self-organization of cyclindrical brushlike polymacromonomers. Single “brush molecules” can be visualized by atomic force microscopy within a monolayer (see picture on the right). This represents a first step towards the production of well-defined nanostructured surfaces with molecular resolution.

The first Sm^IIC σ bonds to be verified by X-ray structure analysis are 2.787(5) and 2.845(5) Å in length. These distances were obtained for a samarium(II) complex in which two C(SiMe₃)₂(SiMe₂ OMe) ligands are each bound to the samarium center through the carbanionic carbon center and the oxygen atom of the methoxy group (see structure depicted on the right). This compound reacts with benzophenone to give the corresponding samarium(III) ketal radical anion complex.

A structural change between a benzoid (1) and a quinoid (2) is possible upon the transfer of two electrons. This finding is supported by cyclic voltammetric and spectroscopic data, and is in agreement with quantum-mechanical calculations on the semiempirical level.

A suitable antimony source for complexes with substituent-free Sb_n ligands is the four-membered ring (tBuSb)₄, which reacts with [{C₅H₅(CO)₃Mo}₂] to yield the tetrahedranes 1 and 2, and with [{C₅Me₅(CO)₃Mo}₂] to give 3. Compounds 2 and 3 are the first complexes to contain the cyclo-Sb₃ ligand. In the crystal they are linked through close SbSb interactions.

A Rh-catalyzed generation of a carbenoid and its intramolecular trapping, followed by a divinylcyclopropane rearrangement and a radical cyclization, are the crucial reactions in a new strategy for constructing the bicyclo[4.3.1]dec-1(9),4-diene-10-one framework of the natural products in the title. The resulting model compound 1 differs from this target core only in the configuration of the quaternary center.

With fluoride as a mineralizing agent, the high-silica zeolites nonasil and ZSM-5 were obtained by hydrothermal syntheses. ²⁹Si NMR spectroscopy showed that five-coordinate silicon exists in the form of SiO_4/2F⁻ in the zeolite frameworks (see the ²⁹Si{¹⁹F} CPMAS NMR spectrum of nonasil on the right). In ZSM-5 at room temperature the fluoride ion undergoes a dynamic exchange between different silicon atoms, which is frozen out at 140 K.

Large differences in the electrostatic properties of nucleosides can have surprisingly small effects on DNA replication. Size and shape appear to be more important, as structural studies of difluorotoluene deoxynucleoside 1, an isostere of thymidine (2), prove. The two nucleosides have virtually the same aromatic ring, almost identical sugar puckers, and very similar glycosidic angles (see the structural formulas). Hydrogen-bonding capacity is apparently not crucial for templating in DNA replication.

A new catalytic route to cyclopropanes from alkenes and diazolakanes is provided by pentacarbonyl(η²-cis-cyclooctene)chromium(0), which generates the catalyst “Cr(CO)₅”. The reactions (1) are characterized by a pronounced chemoselectivity of the participating carbene complex intermediates 1 and allow the unambiguous discrimination of diversely substituted olefins.

Evolution in the test tube: With the help of the error-prone polymerase chain reaction as a method for random mutagenesis, an efficient gene-expression system, and a screening test for the rapid identification of enantioselective catalysts, it is possible to increase sequentially the ee value of an unselective lipase-catalyzed ester hydrolysis (see picture on the right).

Preferentially smaller molecules are oxidized and hydrogenated in the presence of the ultramicroporous (pore diameter < 5.9 Å), platinum-containing (0.5 wt%) heteropolyoxometalate compound Pt/Cs_2.1H_0.9PW₁₂O₄₀, according to studies with methane/2,2-dimethylpropane and ethene/cyclohexene (shown schematically on the right).

The concave inner face of C₆₀ is so inert with respect to the formation of covalent bonds, that even atomic nitrogen in the quartet ground state is stable as an encapsulated guest (shown on the right). Semiempirical calculations and ESR investigations offer an explanation for this unprecedented behavior.