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-yl]acetic acid (1).