Validation Ruls help

HI,

Im using the following code in order to support validation to textBox,currently what I need is very simple

I have a internal list with specific fields ,what I need is to mark the textBox with red boarder when the user

is typing any value that are not in the string list,

This is the first time that i use validation ruls and its not working for me ,The debugger is not invoked in validate method...

any idea how to make it work?

namespace ValidRuls01
{
    public class MyValidationRule : ValidationRule
    {
        public override ValidationResult Validate(object value, CultureInfo cultureInfo)
        {
            List<string> list = new List<String> {"FirstName", "LastName", "BusinessItem", "BusinessItems"};
            bool isValid = list.Any(x => x.Contains(value.ToString()));
            ValidationResult result = null;
            result = isValid ? new ValidationResult(true, null) : new ValidationResult(false, null);
            return result;
        }
    }
}

<Window x:Class="ValidRuls01.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" xmlns:local="clr-namespace:ValidRuls01"
        Title="MainWindow" Height="350" Width="525"><Grid><TextBox x:Name="TextBox1" Margin="208,150,234,143"><TextBox.Text><Binding Path="BoundProperty1" UpdateSourceTrigger="PropertyChanged"><Binding.ValidationRules><local:MyValidationRule  /></Binding.ValidationRules></Binding></TextBox.Text></TextBox></Grid></Window>