Determination of acidic saponins in crude drugs by high- performance liquid chromatography on octadecylsilyl porous glass

High-performance liquid chromatographic (HPLC) analysis on octadecylsilyl porous glass was investigated for acidic saponins in ginseng, bupleurum root and senega. The acidic saponins, malonyl-ginsenosides, malonyl-saikosaponins and senegins, as well as neutral saponins in the crude drugs were separated rapidly by HPLC on this column with aqueous acetonitrile containing KH₂ PO₄ as the mobile phase at room temperature.     

Polymerization of N-carboxy–amino acid anhydrides in the solid state. II. Relation between polymerizability and molecular arrangement in L-leucine NCA and L-alanine NCA crystals

The polymerizability of N-carboxy–amino acid anhydrides (NCAs) of L -leucine and L -alanine was examined in the solid state and in solution. L -leucine NCA shows much higher reactivity in the solid state (when immersed in hexane) than in solution (in acetonitrile), but the opposite is true for L -alanine NCA. However, the two NCAs give similar values of apparent activation energy in each polymerization system. Rather high-molecular-weight polypeptides were obtained in the polymerization of L -leucine NCA in the solid state compared with those obtained in solution, while the molecular weight of polymers obtained from L -alanine NCA was higher in solution than in the solid state. IR spectra showed that α helices form mainly in the polymerization of both L -leucine NCA and L -alanine NCA in the solid state; a small amount of the β structure forms in the latter polymerization. X-ray diffraction and electron microscopy revealed that L -leucine NCA polymerizes predominantly along the c axis in the crystal, while the polymer chains grow in random directions in the crystal of L -alanine NCA. The difference can be explained by the molecular arrangement in the crystal. There are two requirements for high reactivity in the solid state: the five-membered rings of the monomer must form a layer structure and the polymer must occupy nearly the same space as the reacting monomer.     

One-pot synthesis of nitrogen heterocycles initiated by regio- and diastereoselective carbon-carbon bond formation of bifunctional carbonyl compounds

We report a one-pot synthesis of nitrogen heterocyclic compounds initiated by the allylation of the formyl group of bifunctional carbonyl compounds accompanying chemo-, regio-, and diastereoselective carbon-carbon bond formation in side chain moieties.     

Precise Nuclear Quadrupole Moments of 8B and 13B

The electric quadrupole coupling constants eqQ/h of ⁸B (, T _1/2 = 769 ms) and ¹³B (, T _1/2 = 17.4 ms) in single crystal TiO₂ have been precisely measured by the β-NQR technique. The ratios of these Q moments to Q(¹²B) were determined as ∣Q(⁸B)/Q(¹²B)∣ = 4.882(32) and ∣Q(¹³B)/Q(¹²B)∣ = 2.768(24).     

Some basics for operating and analyzing data using the thickness shear mode resonator

The promises of obtaining meaningful measurements on physical systems loading the quartz crystal microbalance are extremely bright. The two aspects of this process, namely the gathering of faithful data and reductions of these data by way of modelling, need careful consideration to avoid some very common missteps which could frustrate this effort. The experimental techniques are emphasized here but a brief introduction to the basic methodologies of modelling is also given.     

A novel, expeditious synthesis of racemic camptothecin

[reaction: see text] A novel and efficient synthesis of racemic camptothecin, starting from a readily accessible hydroxy pyridone, is presented. Key steps include a Claisen rearrangement of a functionalized allylic ether, a hindered Heck coupling, and a Friedl?nder condensation.