UPDATE 2-Onyx sues Bayer over anti-cancer compound

* Onyx says jointly owns anti-cancer compound with Bayer

* Bayer says Onyx has no rights to the substance

* Nexavar among Bayer's top drug hopes (Adds detail on timing of hearing and byline)

By Robert MacMillan

NEW YORK, May 17 (Reuters) - Onyx Pharmaceuticals Inc (ONXX.O) said on Sunday it sued Bayer AG BAYG.DE over its rights to an anti-cancer compound that it says it discovered during joint research with the German drugmaker.

Onyx's lawsuit, filed in the U.S. District Court for the Northern District of California, seeks a declaration that fluoro-sorafenib is a jointly owned collaboration compound under an agreement between the two companies.

Onyx said it learned that the compound is a variant of Nexavar tablets, which Onyx and Bayer co-develop and market.

The company said fluoro-sorafenib has the same chemical structure as Nexavar except that fluoro-sorafenib contains a fluorine atom instead of a hydrogen atom.

"The new molecule had been identified in 1998 during the research collaboration period by the companies' joint research teams," Onyx said in a statement. "Discussions with Bayer regarding Onyx's rights to fluoro-sorafenib under the companies' 1994 collaboration agreement were not productive."