SELECT S.OWNER as SYN_OWNER, S.SYNONYM_NAME as SYN_NAME,
S.TABLE_OWNER as OBJ_OWNER, S.TABLE_NAME as OBJ_NAME,
CASE WHEN O.OWNER is null THEN 'MISSING' ELSE O.STATUS END as OBJ_STATUS,O.STATUS
FROM DBA_SYNONYMS S
LEFT JOIN DBA_OBJECTS O ON S.TABLE_OWNER = O.OWNER AND S.TABLE_NAME = O.OBJECT_NAME
WHERE O.OWNER is null OR O.STATUS != 'VALID';