Go/turn sour
Definition 1 of 3
Pro Tip 1/3Negative Outcome
Use when expressing that something hoped for didn't work out. 
The peace talks between the countries went sour and war ensued.
Pro Tip 2/3Business Failures
Common in business and negotiations that don't end well. 
The merger went sour once the financial discrepancies were discovered.
Pro Tip 3/3Subtle Warning
May imply a gradual process, not always immediate. 
You can sense things might go sour when communication breaks down.