using System;

using System.Globalization;

using System.Text.RegularExpressions;

​

public class Program

{

    public static void Main()

    {

        var dateTime = "2015-04-14 07:30:00 PM";

        dateTime = Regex.Replace(dateTime, @"[^\w:\s-]", ""); //<= this throws an error

        Console.WriteLine(dateTime);

        DateTime dateWithTime = DateTime.ParseExact(dateTime, "yyyy-MM-dd HH:mm:ss tt",

            CultureInfo.InvariantCulture);

        Console.WriteLine("OK");

    }

}