Why? This appears to be a snippet of html. html does use backslashes. Instead it has it own method of converting certain punctuation into what it calls html entities. So double quotes becomes " ;. https://www.php.net/manual/en/function.htmlentities.php
Trying to do this sort of thing with regex is a losing proposition. Basically pretty much any user content needs to be html encoded to avoid breaking your actual html. Template languages such as Twig help automate this.
This is why i asked if his string is JUST the title, or the whole HTML. Because htmlspecialchars isnt going to work if the whole thing is in his string, and you WILL need regex (or a lot of exploding/imploding).