$re = '/\(([^(]+)\)/m';
$str = '[(\'1\',\'Hello is 1)people 2)animals\'), (\'People are 1) hello 2) animals\'), (\'a\')]';
$subst = "[\1]";
$result = preg_replace($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