The present invention provides a novel method for preparing a key intermediate, 3-amino-pentan-1,5-diol (2), which is useful for the preparation of 6-(2,4-difluorophenoxy)-2-[3-hydroxy-1-(2-hydroxyethyl)-propylamino]-8-methyl-8H-pyrido[2,3-d]pyrimidine-7-one (1) a MAP-kinase inhibitor useful in the treatment of rheumatoid arthritis.