A new technique has been invented for constructing chiral drug molecules, report scientists. Chiral molecules are those whose structural complexity allows them to have mirror-image, “left-handed” and “right-handed” forms. For drug molecules, usually only one of those forms works — the other may even have unwanted side-effects — and thus pharmaceutical chemists have a great need for methods to build molecules in a single chiral form, rather than an even mix of both.