Swedish researchers have devised an efficient and practical way to make dendrimers, highly branched polymer-like molecules with a promising future in nanotechnology and biomedicine.

Dendrimers have been known about for almost 30 years, but the difficulty in synthesising these complex molecules has limited their application. Now, Michael Malkoch and colleagues at the Royal Institute of Technology, Stockholm, Sweden, have come up with a way of assembling dendrimers that takes just half the number of steps usually needed.

Until now, the two main methods for making dendrimers used just one sort of branched monomer, which is converted to the dendrimer by repetitive growth and activation steps. But Malkoch's method uses two different monomers alternately, eliminating the need for activation. Not only does this mean that fewer steps are needed to make a dendrimer of a given size, but because both the reactions used are highly efficient, purification is much easier.

Malkoch says that this is a significant advance, because reliable reactions are essential to make such large molecules. The slightest glitches in a sequence of reactions can result in accumulated defects in the final product, he said. A further benefit is that the dendrimers are always ready to react, making the synthesis of derivatives much easier. 

Barry Sharpless, the W M Keck professor of chemistry at the Scripps Research Institute in La Jolla, California, US, is impressed by the work. 'Malkoch and colleagues have provided a beautiful new dendrimer synthesis. It is simple and efficient, and to the best of my knowledge represents the state of the art,' he said.

Malkoch believes that the simplicity and efficiency of the method will increase the commercial availability of dendrimers and thus their prospects for widespread application.

David Barden