Removing Non-alpha Characters && Spaces Script...

Hi I am trying to strip out any non-alpha characters from a field.

i.e. Field = ABC"_IT8*$ should return: ABCIT8

I am writing a loop to do this for all values of a field. The script runs, but hangs....please could somebody advise on the code below...:

I run the script but it doesn't seem to finish. Can anybody see any issues with the code:

DECLARE @Index SMALLINT,
@MATCH_Supplier_name varchar(500),
@Counter numeric,
@Max numeric
-- @sqlstring varchar(500)

SET @Counter = 1
SET @Max = (SELECT Max(DTect_Supplier_SRN) FROM SUPPLIER_TABLE_TEST)

WHILE @Counter <@Max
BEGIN
SET @MATCH_Supplier_name = (SELECT Match_Supplier_Name FROM SUPPLIER_TABLE_TEST WHERE @Counter = DTect_Supplier_SRN)
SET @Index = LEN(@MATCH_Supplier_name)
WHILE @Index > = 1
SET @MATCH_Supplier_name = CASE
WHEN SUBSTRING(@MATCH_Supplier_name, @Index, 1) LIKE '[a-zA-Z]' TH EN SUBSTRING(@MATCH_Supplier_name, @Index, 1)
WHEN SUBSTRING(@MATCH_Supplier_name, @Index, 1) LIKE '[0-9]' THEN SUBSTRING(@MATCH_Supplier_name, @Index, 1)
ELSE ''
END + @MATCH_Supplier_name
SET @Index = @Index - 1
--PRINT @MATCH_Supplier_name
SET @Counter = @Counter + 1
END