TSQL CASE WHEN THEN SYNTAX - USING REPLACE

This actually applies to a prior question, TSQL 2008 USING LTRIM(RTRIM and Still Have Spaces

I am at the point of writing a very lengthy SELECT statement using OMG PONIES statement to remove NON NULL non visible characters

 (WHEN PropStreetAddr is NOT NULL THEN
    (SELECT LTRIM(RTRIM((REPLACE(PropStreetAddr, 
                                 SUBSTRING(PropStreetAddr, 
                                           PATINDEX('%[^a-zA-Z0-9 '''''']%', 
                                           PropStreetAddr), 
                           开发者_如何转开发      1), '') AS PropStreetAddr)

Query:

SELECT 
  CASE WHEN LOAN_NUMBER IS NOT NULL THEN 
     REPLACE( LOAN_NUMBER,SUBSTRING (LOAN_NUMBER,PATINDEX( ' %[^a-zA-Z0-9 '''''']% ' , ' ' ) as LOAN_NUMBER.
 ,CASE WHEN MERS_ID IS NOT NULL THEN 
     REPLACE(  MERS_ID,SUBSTRING (MERS_ID,PATINDEX( '  %[^a-zA-Z0-9 '''''']% ' , ' ' ) as MERS_ID 
 ...127 more lines of similar statements

As soon as I check the syntax I receive this error pointing to the first Case statement after SELECT:

Msg 156, Level 15, State 1, Line 143 Incorrect syntax near the keyword 'as'.

Could someone help me understand what I am missing?

---

You're missing the END from your case statements. You look like you could do with ELSEs in there as well, although these are not compulsory - if left off and nothing matches then you'll get a NULL.

CASE
 WHEN something then value1
 WHEN somethingelse then value2
 ELSE value3
END

---

You are missing some right parrens.