Using regex to extract username from email address

My string of text looks like this:

johndoe@domain.com (John Doe)

I need to get just the part before the @ and nothing else. The text is coming from a simple XML object if that matters any.

The code I have looks like this:

$authorpre = $key->{"author"};
$re1 = '((?:[a-z][a-z]+))';

if ($c = preg_match_all ("/".$re1."/is", $authorpre, $matches))
{
    $author = $matches[1][0];
}

Sometimes the username might have numbers or an underscore before the @ symbol, which is where the regex stops it seems.