$re = '/^(?<token>"[^"]+"\s*:\s*)(?:\d*[^\d:][^:]*:)*(?<number>\d+)(?::[^:]*)*$/';
$str = '"number":4aac4c35-8e3e-4730-8364-381884d6f20f:DA:OPAS:117804471:PAN:false';
$subst = "$1$2";
$result = preg_replace($re, $subst, $str, 1);
echo "The result of the substitution is ".$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