php替换以小写字母结尾的单词末尾的逗号

I have a string like this: 2D-Digital, 1:10PM, 3:10PM, RealD-3D, 5:15PM What I need is a string like this 2D-Digital: 1:10PM, 3:10PM, RealD-3D: 5:15PM

I thought about using preg_replace on the string to find the words that end with a letter and then replace the , into a : but the problem with that is the 3:10PM and such also end with a letter. Please help me.

You can use a negative and positive look-behind to find the desire commas :

(?<![AP]M)(?<=[a-zA-Z]),

see demo https://regex101.com/r/hD7bE6/2