General synonyms:
* Reach a peak
* Reach a climax
* Reach a high point
* End
* Conclude
* Result in
* Lead to
* Apex
* Summit
* Pinacle
More specific synonyms:
* Mature (for growth or development)
* Issue (for a process)
* Culminate in (for an event)
The best synonym for "culminate" will depend on the specific sentence or context.