All four diastereoisomers of 4-hydroxypipecolic acid were prepared in a form conveniently protected for drug discovery applications with the use of industrially scaleable methodology. Resolution of the racemic starting material using proprietary acylases followed by an acyliminium ion cyclisation gave diastereomeric mixtures of 4-formyloxypipecolic acid, which were differentiated using an enzyme-catalysed hydrolysis. The products were separated by partition, and by following a sequence of straightforward chemical steps, the individual stereoisomers of the protected 4-hydroxypipecolates were crystallized to optical purity in 100 g quantities.