A novel tyrosyl tRNA synthetase inhibitor, SB-219383, has been isolated from a Micromonospora sp. The structure of SB-219383 has been elucidated by a combination of derivatisation, spectroscopic and other analytical techniques and found to be N-(L-tyrosyl)-2-amino[1(S*),3(S*),4(S*),5(R*),8(R*)-2,4,5,8-tetrahydroxy -7-oxa-2-azabicyclo[3.2.1]oct-3-y1]acetic acid (1).