Organic reactions in frozen water: Michael addition of amines and thiols to the dehydroalanine side chain of nocathiacins

Nocathiacins are densely functionalized cyclic thiazolyl peptide natural products with potent in vitro and in vivo antibacterial activity against a variety of gram-positive bacteria, including a number of multiple drug-resistant strains. Attempts to prepare Michael adducts using known conditions resulted in the formation of complex mixture of products. In order to overcome this problem, we developed unique conditions in which Michael addition of amine and thiol nucleophiles to the dehydroalanine moiety of nocathiacins was successfully achieved in frozen water. Under these conditions, the Michael addition was highly chemoselective, very efficient and provided good isolated yields of the desired products.     

新鲜植物样品的冷冻制样技术

为电子显微分析提供一种制备新鲜植物样品的方法，样品经过琼脂包埋，冷冻断裂，真空干燥处理，完好地保持了植物原来的自然结构，化学成分以及他们的对应关系。     

Incorporation and release behavior of amitriptylene in core-shell-corona type triblock copolymer micelles

A cationic antidepressant drug, amitriptylene (AMT), was successfully incorporated into core-shell-corona micelles of poly[styrene-b-sodium 2-(acrylamido)-2-methyl-1-propanesulfonate-b-ethylene oxide] (PS-b-PAMPS-b-PEO). Zeta-potential measurements revealed that both electrostatic and hydrophobic interactions contributed to the binding of the drug to the polymer. The AMT/PS-b-PAMPS-b-PEO nanocomplexes were characterized by dynamic light scattering, scanning electron microscopy, and transmission electron microscopy. The hydrodynamic diameter of the AMT loaded nanocomplexes decreased from 80 to 40nm depending on the amount of the drug loaded on the polymer. This is attributed to the cancellation of the negative charge of the PAMPS group by the cationic drug. The AMT/PS-b-PAMPS-b-PEO nanocomplexes were stable in aqueous solution exhibiting no aggregation or no precipitation for several months. Release of the AMT from the nanocomplexes was investigated in vitro in salt-free and 0.1M NaCl solutions. The drug was released faster in the 0.1M NaCl solution than in the salt-free solution. This is due to the shielding effect of the salt on the electrostatic interaction. However, in both cases, the drug release mainly occurs by the Fickian diffusion mechanism.