Sort Excel columns in C#

Excel.Range excelcol = (Excel.Range)Worksheet.get_Range("B" + Worksheet.Rows.Count, Type.Missing);
             int lastrow= mulsortop.get_End(Microsoft.Office.Interop.Excel.XlDirection.xlUp).Row;              Excel.Range 2key = Worksheet.get_Range("B5:B" + lastrow);
    Excel.Range key = Worksheet.get_Range("BM5:BM" + lastrow);
    Worksheet.Sort.SortFields.Clear();
    Worksheet.Sort.SortFields.Add(2key// Second Key
                             , Excel.XlSortOn.xlSortOnValues
                             , Excel.XlSortOrder.xlAscending
                             , Type.Missing
                             , Excel.XlSortDataOption.xlSortNormal);
    destworkSheet.Sort.SortFields.Add(key// First Key
                             , Excel.XlSortOn.xlSortOnValues
                             , Excel.XlSortOrder.xlAscending
                             , Type.Missing
                             , Excel.XlSortDataOption.xlSortNormal);
    Worksheet.Activate();
    Worksheet.Sort.SetRange(Worksheet.get_Range("B5:BQ" + lastrow));
    Worksheet.Sort.Header = Excel.XlYesNoGuess.xlNo;
    Worksheet.Sort.MatchCase = false;
    Worksheet.Sort.Orientation = Excel.XlSortOrientation.xlSortColumns;
    Worksheet.Sort.SortMethod = Excel.XlSortMethod.xlPinYin;
    Worksheet.Sort.Apply();