The cis-cyclobutyl group is an effective replacement for the chiral linking group required in hydroxyureas for good in vivo activity against 5-lipoxygenase. The principle is illustrated in two 5-LO inhibitors: 858C, a more potent inhibitor than Zileuton and, 862C, a very potent 5-LO inhibitor with good oral persistence. Leukotrienes are thought to be implicated in a variety of pathophysiological states in man, particularly those involving inflammation. Reduction of leukotriene biosynthesis via inhibition of arachidonate 5-lipoxygenase (5-LO) offers a possible new approach to combating these diseases and is currently the focus of several groups. To date, Zileuton is the most advanced selective 5-LO inhibitor in clinical development and, although Zileuton is not the most potent or most in vivo persistent 5-LO inhibitor known, it has nevertheless shown promising activity in asthma. We have previously reported our discovery at Wellcome of the N-hydroxyurea 70C which is a very potent 5-LO inhibitor in vitro and has a long duration of action in vivo following oral administration. 70C was designed to have a favourable metabolic profile, compared with earlier compounds, by the introduction of a F-atom and a-methyl groups. However, the a-methyl group present in 70C (necessary to block oxidation) introduces a chiral centre into the molecule. Zileuton also contains an a-methyl group in the link between the hydroxyurea and aromatic group. Indeed, an earlier report from the Abbott group noted that an a-methyl group enhanced in vivo potency in a series of benzyl acetohydroxamates. Although the (R)-and (S)-enantiomers of 70C have similar activity against 5-LO, the (S)-enantiomer is cleared more rapidly in vivo. This enantioselective metabolism property is likely to be present in other members of the N-hydroxyurea/hydroxamate class of 5-LO inhibitors. In view of the complications involved in development of enantiomers with different properties it would be desirable to remove chirality. Thus, we report here how we have been able to replace the chiral linker group, in 70C and Zileuton, with the cis-cyclobutyl group, substituted via the 1- and 3-positions, to obtain novel achiral 5-LO inhibitors. The principle is illustrated in 858C, where in vitro potency against 5-LO has been improved over Zileuton, and in 862C, where high potency and persistent in vivo activity against 5-LO via oral administration is achieved.