using System;

using System.Text.RegularExpressions;

//using Newtonsoft.Json.Linq;

using Newtonsoft.Json;

using System.IO;

​

​

public class Program

{

    public static void Main()

    {

        string input = "Field1 : 123 , Field2 : 456";

        string output = "";

        string[] substrings = Regex.Split(input, ",");

        foreach (string match in substrings)

        {

            string[] tmp = Regex.Split(match, ":");

            output = output + "\"" + tmp[0].ToString().Trim() + "\":" +  tmp[1].ToString().Trim() + "," ;

        }

        Fields flds = JsonConvert.DeserializeObject<Fields>("{" + output.TrimEnd(',') + "}");

        Console.WriteLine("Field1=" + flds.Field1 + ", Field2=" + flds.Field2);

    }

    public class Fields

    {

        public string Field1 { get; set; }

        public string Field2 { get; set; }

    }

}