$re = '/\s*(\w+)\.Append\((.*?)\);/';
$str = 'sb.Append(@\\"first string to append(1) \\"); sb.Append(\\"second string to append(2)\\");';
$subst = "[$1 appendString: $2];";
$result = preg_replace($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