using System;

using System.Text.RegularExpressions;

public class Program

{

    public static void Main()

    {

        string text = "<p>This is a \"wonderful long text\". \"Another wonderful ong text\"</p> At least it should be. Here we have a <a href=\"http://wwww.site-to-nowhere.com\" target=\"_blank\">link</a>";

        Console.WriteLine(text);

​

        Regex rx = new Regex("<.*?>");

​

        string result = rx.Replace(text, new MatchEvaluator(ReplaceLink)).Replace("\"", "&" + "quot;");

        Console.WriteLine(result);

    }

    static string ReplaceLink(Match m)

    {

        return m.ToString().Replace("\"", "'");

    }

}