Case sensitive not working :(

string input = TextBox1.Text;
Dictionary<string, string> map = new Dictionary<string, string>();
map.Add("go", "GYO");
map.Add("GO", "OMO");
map.Add("Go", "OIO");

string temp = input;
foreach (var entry in map)
{
    string key = entry.Key;
    string value = entry.Value;
    temp = Regex.Replace(temp, key, match =>
    {
        bool isUpper = char.IsUpper(match.Value[0]);

        char[] result = value.ToCharArray();
        result[0] = isUpper
            ? char.ToUpper(result[0])
            : char.ToLower(result[0]);
        return new string(result);
    }, RegexOptions.Compiled);

Tried all RegexOptions