Written by Dr. Sharbil J. Firsan

Nitroxyl (H–N=O), the reduced form of nitric oxide (NO), a well-established biological signaling agent, is beginning to show potential as a therapeutic agent for treating heart congestion, a condition that leads to tens of thousands of deaths each year.  However, the lack of HNO-specific detection methods have hampered the study of the role it plays in biological systems.
    The study highlighted here is one attempt at developing such a detection method.  It takes advantage of the ready formation of an aza-ylide from the reaction of triphenylphosphine, tris(4,6-dimethyl-3-sulfonatophenyl)phosphine, or similar triarylphosphine with HNO in dioxane–water or in TRIS buffer.  When the aza-ylide is generated in the presence of a suitably positioned electrophilic ester group, it undergoes the Staudinger ligation to form the corresponding amide, effectively trapping HNO.

Reisz, J. A.; Klorig, E. B.; Wright, M. W.; King, S. B. Org. Lett. 2009, 11, 2719.

Written by Dr. William Sommer, product line manager for Catalysis 

Aldrich had the pleasure to welcome Professor Ei-ichi Negishi, from Purdue University, last September in Milwaukee. Professor Negishi talked about the ZACA catalyst and the different applications associated with it. This is a 7-part video that lasts approximately 1 hour.

http://tr.im/rLY0

 If you want to see more of these types of webcasts, please leave a comment or contact us at chemblogs@sial.com

Enjoy, your feedback is welcomed

Written By: Mark Redlich, Ph.D.

I just came across an ASAP article on Organic Letters which describes a clean and fast aziridination of diazoacetamides with imines.  Typically, yields and chemoselectivities of Lewis or Brønsted acid catalyzed asymmetric aziridinations of N-Boc-imines have been modest. Zhong and coworkers achieved excellent results when a chiral phosphoric acid derived from anthryl-substituted (R)-BINOL was used as the catalyst.  In these cases, the reactions were all completed in 10 minutes at room temperature, providing high yields and displaying excellent chemo-, diastereo-, and enantioselectivities.

 
Zeng, X. et al. Org. Lett. 2009, ASAP.

Chatani and coworkers have reported a complementary method to the Sonogashira-coupling for the alkynylation of the ortho C-H bond of various anilides. In the presence of catalytic Pd(OAc)₂, AgOTf, and K₂CO₃, ortho-C-H-bond metalation takes place (stoichiometric evidence for this palladacycle), followed by addition of the Pd-intermediate to the bromo alkyne, generating a vinyl palladium species, which upon beta-bromo-elimination generates the alkynylated product. It should be noted that ligand exchange of the bromide for triflate is necessary to generate a species capable of electrophilic metalation on the substrate. A variety of substrates can be utilized in this transformation, providing unprecedented molecular complexity and flexibility for alkynylations of aromatic substrates. In addition, the –Si(i-Pr)₃ provides an additional functional group handle for further manipulation.

Tobisu, M.; Ano, Y.; Chatani, N. Org. Lett. 2009, ASAP.