The Negative Side of Boran

According to researchers Makoto Yamashita and his colleagues at the University of Tokyo, Japan, a molecule that hosts a negatively-charged boron atom could prove to be an exciting addition to the chemist's toolbox. Recently they have isolated the anion as its lithium salt.  

Lithium can partner with many boron's neighbors in the periodic table, such as nitrogen in lithium amide and carbon in methyllithium. However, there have been no direct observations of the equivalent boryllithium compounds containing a negative boron atom.

 

This type of boron anion shares the same number of valence electrons as its popular carbon cousin, the N-heterocyclic carbene. The Tokyo team demonstrated boryllithium's nucleophilic prowess in reactions with n-butyl chloride and benzaldehyde.

This work opens the door to new pathways in boron chemistry that will substantially impact organic synthesis in general.

Ref: Makoto Yamashita and colleagues at the University of Tokyo, Japan. Science 2006, 314, 113.

Identification of novel therapeutic targets for HIV

Using a functional genomic screen, researchers at Harvard Medical School have identified 273 proteins that the AIDS virus needs to survive in human cells, opening up new potential targets for drugs. Their work, published online on 10th Jan. by Science, used RNA interference to screen thousands of protein-making genes; previously, scientists had identified only 36 human proteins that the virus uses to break into cells, hijack their machinery and start reproducing. 

    The virus, which is itself only a short string of genetic material inside a protective capsule, can make only 15 proteins, so it has to adopt human proteins to its own use. Many of the proteins identified by the screen are already known to be important to cells in the immune system, which is the port of entry for H.I.V.

xDNA: A New Genetic System?

Professor Eric Kool and his co-workers have developed " eXpanded DNA " dubbed "xDNA". The synthetic xDNA is expanding by adding benzene molecule to the base on the nucleotides and is a bit longer than the regular 'B' form.


Unlike natural DNA, the expanded DNA is fluorescent and is considerably more stable when subjected to higher temperatures. Its unusual fluorescent properties could make it useful as a probe or diagnostic marker.

Is xDNA also capable of replicating? That is something Kool hopes to find out. Experiments with xDNA are expected to provide new insight into the behavior of natural DNA.

Ref: E. Kool, et al. Angew. Chem Int. Ed., 44, 3118-3122 (2005), JACS , 128, 9219-9230 (2006).

The solvent makes the difference

The solvent surrounding the chiral molecule creates a chiral shell (Chiral Imprint). The chiroptical properties can originate mainly from the chiral solvent shell rather than from the chiral solute. For example, (S)-methyloxirane has a positive optical rotation in water but has a relatively strong negative value in benzene (P. Mukhopadhyay et al. Angew Chem Int Ed 2007, 46, 6450-6452).

 

Computational experiments by J Neugebauer (Angew Chem Int Ed 2007, 46, 7738-7740) shows the presence of the solute imprints a chiral structure on the inner solvation shell.

Cyanation of aryl halides

There are several methods available for the cyanation of aryl halides. However, a common problem with many of the more traditional methods is that they are very toxic# One method to full fill these criteria has been around for a while (Weissman S A et al., J. Org. Chem.2005, 70, 1508-1510.)

  Figure: Ligand-free, palladium-catalyzed cyanation of aryl halides. 

Potassium hexacyanoferrate(II) has been used as a cyanide source. This result increases the list of metal-catalyzed reactions that can be performed without ligand.

This method's advantage is obvious; in contrast to other cyanating agents, potassium hexacyanoferrate(II) is less poisonous# and can be handle without special precaution due to the slow release of cyanide ions. Additionally, it significantly improved catalytic productivity compared to know procedures achieved previously.

#( KCN is extremely toxic (LDL0(oral, human) =2.86mg Kg-1 and develop HCN on contract with acidic water. K4[Fe(CN)6]­ is non-toxic and used in the food industry for metal precipitation in wine. Also, it has been used as an anti-agglutinating auxiliary for NaCl (table salt). It is soluble in water without decomposition. Schareina T et al, Chem Commun., 2004, 1388-1389.)