Synthetic studies of kampanols, novel p21 farnesyltransferase inhibitors: an efficient synthesis of the tetracyclic ABCD ring system of kampanols

An enantioselective synthesis of the tetracyclic ABCD ring system (4) of kampanols, novel Ras farnesyltransferase inhibitors from a microorganism, was efficiently achieved for the first time starting from the known trans-decalone derivative 9. The synthetic method involves the following two key steps: (i) a conjugate addition reaction between the α-methylene ketone 6 and the Grignard reagent (7) of the ortho-disubstituted bromobenzene derivative 8 to deliver the coupling product 21 with stereoselectivity at the C9 position and (ii) a phenylselenium-mediated cyclization reaction of the phenol derivative 5 to stereoselectively construct the requisite tetracyclic intermediate 25 possessing the cis-fused connectivity of the B/C rings.     

Hierarchical polymer assemblies constructed by the mutual template effect of cationic polymer complex and anionic supramolecular nanofiber

Creation of higher-ordered polymeric architectures composed of alternative assemblies of single-walled carbon nanotubes (SWNTs) and fibrous porphyrin J-aggregates can be easily achieved utilizing the cationic semi-artificial polysaccharide which can act not only as a tubular host for SWNTs but also as a one-dimensional template for porphyrin molecules. This new class of hierarchical polymer assembly is formed, for the first time, by the mutual template effect of two components, i.e., the cationic SWNT complexes and the anionic porphyrin supramolecular nanofibers. In the present system, the self-assembling behaviors of the SWNT complexes as well as the final properties of the SWNT nanoarchitectures are strongly affected by the packing mode of porphyrin molecules on the cationic semi-artificial polysaccharide. Furthermore, we have confirmed that the light energy captured by the porphyrin J-aggregates is effectively transferred to SWNTs.     

Alternate layer-by-layer adsorption of single- and double-walled carbon nanotubes wrapped by functionalized beta-1,3-glucan polysaccharides

A great deal of attention has been focused on exploiting novel methods to fabricate thin carbonaceous capsules from multiple components for advanced materials. A layer-by-layer (LbL) method is therefore being introduced to synthesize thin and multi-carbon nanotube (CNT)-based hollow capsules from CNT complexes with cationic or anionic complementarily functionalized beta-1,3-glucans as building-blocks. These ionic beta-1,3-glucans wrap around single-walled carbon nanotubes (SWNTs) and double-walled carbon nanotubes (DWNTs) to form water-soluble complexes with ionic groups on their exterior surface. Alternate self-assembly of these CNT complexes on the silica particles is demonstrated in solution by electrostatic interactions. The LbL adsorption processes were carefully monitored by zeta-potential measurements, frequency shifts of a quartz crystal microbalance (QCM), and electron micrographs. Silica particles were then dissolved away by HF acid to obtain CNT-based hollow capsules composed of SWNTs and DWNTs. We believe that these novel surface adsorption methods are useful for potential design of CNT-based advanced functional materials.     

Total Synthesis of (±)‐Phomoidride D

Described herein is a synthetic strategy for the total synthesis of (±)‐phomoidride D. This highly efficient and stereoselective approach provides rapid assembly of the carbocyclic core by way of a tandem phenolic oxidation/intramolecular Diels–Alder cycloaddition. A subsequent SmI₂‐mediated cyclization cascade delivers an isotwistane intermediate poised for a Wharton fragmentation that unveils the requisite bicyclo[4.3.1]decene skeleton and sets the stage for synthesis completion.     

Enantioselective total synthesis of (-)-candelalide A, a novel blocker of the voltage-gated potassium channel Kv1.3 for an immunosuppressive agent

A convergent route to (-)-candelalide A involved the union of a trans-decalin portion (AB ring) and a gamma-pyrone moiety through the C16-C3' bond to assemble the whole carbon framework and subsequent formation of the dihydropyran ring (C ring) as the crucial steps. A strategic [2,3]-Wittig rearrangement was employed for establishing the stereogenic center at C9 and an exo-methylene function at C8 present in the decalin portion. [reaction: see text]     

Schizophyllans carrying oligosaccharide appendages as potential candidates for cell-targeted antisense carrier

Schizophyllans carrying beta-lactoside and alpha-mannoside appendages were prepared from native schizophyllan through NaIO4 oxidation followed by reductive amination using aminoethyl-beta-lactoside and alpha-mannoside, respectively. The resulting schizophyllans form stable macromolecular complexes with polynucleotides, such as poly(C) and poly(dA). Specific affinity between these macromolecular complexes and saccharide-binding proteins was demonstrated by surface plasmon resonance and agarose gel staining assays. beta-lactoside-appended schizophyllan enhanced an antisense activity in hepatocytes which express lactoside-binding proteins on their cell surfaces.     

Experimental evidence for intramolecular blue-shifting C-H...O hydrogen bonding by matrix-isolation infrared spectroscopy

Experimental evidence for intramolecular blue-shifting C-H...O hydrogen bonding is presented. Argon matrix-isolation infrared spectra of 1-methoxy-2-(dimethylamino)ethane exhibit a band at 3016.5 cm-1. Spectral behavior with annealing indicates that this band is assigned to the most stable conformer, trans-gauche-(trans|gauche'), with an intramolecular C-H...O hydrogen bond. Density functional calculations show that this band arises from the stretching vibration of the C-H bond participating in the formation of the C-H...O hydrogen bond. The C-H bond is shortened by 0.004 A, and the C-H stretching band is blue-shifted by at least 35 cm-1 on the formation of the hydrogen bond. The (C)H...O distance is calculated as 2.38 A, which is shorter than the corresponding van der Waals separation by 0.3 A.     

Synthetic studies toward GKK1032s, novel antibiotic antitumor agents: enantioselective synthesis of the fully elaborated tricyclic core via an intramolecular Diels-Alder cycloaddition

An enantioselective synthesis of the fully elaborated tricyclic decahydrofluorene core (ABC-ring system) of GKK1032s, novel antimicrobial and antitumor agents, has been accomplished for the first time by employing a highly diastereoselective intramolecular Diels-Alder (IMDA) reaction. The key substrate for the IMDA reaction was efficiently prepared through (i) an intermolecular Diels-Alder reaction between a siloxydiene and an optically active enone derived from D-mannitol to construct the appropriately functionalized C-ring and (ii) CuCl-promoted Stille coupling of an (E)-vinyl iodide and a vinylstannane to install the requisite triene side chain as the crucial steps.