Polyhydroxyalkanoates made diastereoselectively

Polyhydroxyalkanoates (PHAs) are poised to be the next big thing in biodegradable polymers. That’s because PHAs don’t need to go to industrial composting facilities to degrade. Instead, they break down in ambient environments, even in the ocean. PHAs are made industrially with bacteria via fermentation, but the process can be slow and expensive. Eugene Y.-X. Chen and coworkers at Colorado State University have been working on a chemical approach to PHAs, which offers a more efficient route to these polymers. Last year, Chen’s team reported using eight-membered cyclic diolide monomers that are derived from succinate, a renewable resource, to synthesize a PHA with a pendant methyl group (Nat. Commun. 2018, DOI: 10.1038/s41467-018-04734-3). The problem, he says, is that they lost significant amounts of starting material because they had to separate diastereomeric monomers. Now, Chen and colleagues have developed a new, diastereoselective polymerization methodology (Science 2019, DOI: 10.1126/science.aax8466). It uses yttrium and lanthanum catalysts that selectively react with racemic monomers before they react with meso monomers, eliminating the need to separate diastereomers (shown). The resulting block polymers have better properties than PHAs made from either purely racemic or meso cyclic diolides. Chen’s team can even tune PHA properties by using diastereomeric cyclic diolides with different substituents in one pot.