Remove special character and numbers from string in sql server

declare @str varchar(20)
set @str='ab12#89L(h12k'
Select @str as 'Original String'
declare @temp_str varchar(20), @i int
select @temp_str ='',@i=1
while @i<=len(@str)
begin
    set @temp_str=@temp_str+case when substring(@str,@i,1) like '[a-zA-Z]' then substring(@str,@i,1) else '' end
    set @i=@i+1
end
select @temp_str as 'String with Alphabets'