CREATE FUNCTION dbo.UDF_ParseAlphaNumChars
(
@string VARCHAR(8000)
)
RETURNS VARCHAR(8000)
AS
BEGIN
 DECLARE @IncorrectCharLoc SMALLINT
 SET @IncorrectCharLoc = PATINDEX('%[^0-9A-Za-z]%', @string)
 WHILE @IncorrectCharLoc > 0
 BEGIN
  SET @string = STUFF(@string, @IncorrectCharLoc, 1, '')
  SET @IncorrectCharLoc = PATINDEX('%[^0-9A-Za-z]%', @string)
 END
 SET @string = LTRIM(RTRIM(REPLACE(@string,' ','')))
 RETURN @string
END
GO

—-Test
SELECT dbo.UDF_ParseAlphaNumChars('ABC”_I+{D[]}4|:e;””5,<.F>/?6')
GO