$re = '/,(?![^()]*\))\s*/';
$str = 'abc, 3rncd (23uh, sdfuh), 32h(q23q)89 (as), dwe8h, edt (1,wer,345,rtz,tr t), nope';
$subst = "\n";
$result = preg_replace($re, $subst, $str);
echo "The result of the substitution is ".$result;
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php