CGRP antagonists useful as tracer compounds for positron emission tomography

The present invention provides a compound of Formula I or a pharmaceutically acceptable salt thereof: wherein R1 is hydrogen, F or 18F; and R2 is hydrogen, F or 18F; with the proviso that when R1 is 18F then R2 is not 18F, which is useful as a CGRP receptor antagonist for PET imaging. 本发明提供式I的化合物或其可药用盐：其中R1是氢、F或18F；和R2是氢、F或18F；条件是当R1是18F时，则R2不是18F，其可用作用于PET成像的CGRP受体拮抗剂。