$re = '/^(?!<div>)(.*)$/m';
$str = '<div>Lorem ipsum.</div> - эту строку не надо;
Lorem ipsum. - эту строку надо;
<li>Lorem ipsum.</li> - и эту строку надо;
<div>Lorem ipsum.</div> - эт у не надо.';
preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0);
// Print the entire match result
var_dump($matches);
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