13C nuclear magnetic resonance spectroscopy of atisine and veatchine-type C20-diterpenoid alkaloids from aconitum and garrya species

¹³C NMR spectra of the atisine- and veatchine-type alkaloids, as well as certain of their derivatives, have been obtained by the Fourier transform technique at 25.03 MHz. With the help of single-frequency off-resonance proton decoupling techniques, additivity relationships, and the effects induced by certain structural changes, self-consistent assignments of nearly all the resonances have been made. The ¹³C NMR spectra are also analyzed to identify skeletal features of the atisine and veatchine-type alkaloids of use in the structure determination of new C₂₀-diterpenoid alkaloids. On the basis of the ¹³C NMR analysis of atisine and veatchine as well as a temperature-dependence study of atisine, the existence of C-20 epimers in these alkaloids is demonstrated. A ¹³C NMR study of the behavior of the oxazolidine ring of atisine in non-ionic and ionic solvents indicates that the C-20 epimers of atisine do not exist in an equilibrium mixture in solution and are not interconvertible via a zwitterion as reported earlier.     

Structure of actin cross-linked with alpha-actinin: a network of bundles

Three-dimensional laser scanning confocal microscopy has revealed that filamentous actin, when complexed with the cross-linking protein alpha-actinin, will spontaneously assemble on a micron scale into a structure comprised of a relatively rigid, frequently branching, 3D network of bundles with characteristic mesh size of the order of the persistence length of F-actin. In contrast, additional nanoscale ordering is observed, as synchrotron x-ray diffraction has revealed a disordered, distorted square lattice of actin fibers within the individual bundles.     

Zeeman effect of the 6011 Å line of Pr3+: LaCl3 using the fluorescence line-narrowing technique

The Zeeman effect of the 6011 Å resonance line of Pr³⁺ in a LaCl₃ crystal has been studied by means of the fluorescence line-narrowing technique using a cw single-mode tunable laser. The experiments have confirmed the assumptions made previously to interpret the spectra in zero magnetic field. They have led to accurate values of the hyperfine structure constant and of the spectroscopic splitting g-factor of the ground level.     

Crytocaryone: A revised structure

Cryptocaryone, formulated earlier as the chalcone 1, has been shown to have structure 2 by an X-ray crystallographic analysis. Carbon-13 assignments are given.     

An unusual oxidation of an NCH3 group to an NCHO group by osmium tetroxide

Treatment of pyrodelphinine (1) with osmium tetroxide afforded a mixture of the cis-hydroxylation product 2 and an unexpected product 3 in the ratio of 4:1, respectively. Similarly, oxidation of delphinine (5) afforded α-oxodelphinine (6; 75%) and oxidation of mesaconitine (8) furnished oxonitine (9; 92%). Thus a very selective oxidation of the N-methyl group of delphinine and mesaconitine is effected osmium tetroxide.     

Low temperature electrical transport in n-type lead telluride

The high mobilities observed at low temperatures in n-type annealed lead telluride samples are greater than those usually found and calculated. This involves the change of the dielectric constant value (400) and to take into account the compensation by impurities which limits the mobility at low concentrations.     

Investigation of a new thermosensitive block copolymer micelle: hydrolysis, disruption, and release

Thermosensitive polymer micelles are generally obtained with block copolymers in which one block exhibits a lower critical solution temperature in aqueous solution. We investigate a different design that is based on the use of one block bearing a thermally labile side group, whose hydrolysis upon heating shifts the hydrophilic-hydrophobic balance toward the destabilization of block copolymer micelles. Atom transfer radical polymerization was utilized to synthesize a series of diblock copolymers composed of hydrophilic poly(ethylene oxide) (PEO) and hydrophobic poly(2-tetrahydropyranyl methacrylate) (PTHPMA). We show that micelles of PEO-b-PTHPMA in aqueous solution can be destabilized as a result of the thermosensitive hydrolytic cleavage of tetrahydropyranyl (THP) groups that transforms PTHPMA into hydrophilic poly(methacrylic acid). The three related processes occurring in aqueous solution, namely, hydrolytic cleavage of THP, destabilization of micelles, and release of loaded Nile Red (NR), were investigated simultaneously using 1H NMR, dynamic light scattering, and fluorescence spectroscopy, respectively. At 80 degrees C, the results suggest that the three events proceed with a similar kinetics. Although slower than at elevated temperatures, the disruption of PEO-b-PTHPMA micelles can take place at the body temperature (approximately 37 degrees C), and the release kinetics of NR can be adjusted by changing the relative lengths of the two blocks or the pH of the solution.     

A general method for alkylating 2(5H)-furanones; reduction of products to 3-, 2,3-, and 3,4-substituted furans

The cycloaddition of diazoalkanes, diazoesters and diazoketones to 2(5H)-furanones followed by thermal decomposition of the respective adducts is shown to provide a general method for the preparation of a variety of alkylated 2(5H)-furanones. Reduction of the latter compounds with diisobutylaluminum hydride affords the corresponding substituted furans in good yield.