using System;

using System.Text.RegularExpressions;

​

public class Program

{

    public static readonly Regex LinkSubstitutionRegex = new Regex(@"<a[^>]+?href=""([^""]+)""[^>]*>(?<content>[\S\s]+?(?=</a>))</a>", RegexOptions.Compiled);

​

    public static void Main()

    {

        var link = @"Hello Chris <a href=""http://sites.vuturevx.UNL-002:9090/email_handler.aspx?sid=cea6c613-81bf-42e4-83ea-f2d5eaf3c7ff&redirect=http%3a%2f%2fwww.dentons.com"" style=""-webkit-text-size-adjust:none;color:#000001;text-decoration:underline"">dentons.com</a>";

        var output = LinkSubstitutionRegex.Replace(link,"www.google.com");

            Console.WriteLine(output);

    }

}