My code doesn't work with second level tld's like domain.co.uk

The strainge thing is, that it works in php with preg_match() ^^

Here is my conf:

  # add www.
  if ($host ~ ^(?!www)) {
   rewrite ^/(.*)$ http://www.$host/$1 permanent;
  }

  # remove subdomain
  if ($host ~ "^www\.(.*)\.(.*\.([a-z]{2,4}|[a-z]{2}\.[a-z]{2}))") {
   set $host_without_sub $2;
   rewrite ^/(.*)$ http://www.$host_without_sub/$1 permanent;
  }