Try this
declare @s-2 varchar(8000) ='SENT REQUEST TO BREC TO VALADATE. WHY OOA LETTER WAS SENT. PER'
select stuff(
(select '.'+upper(left(item,cappos))+lower(substring(item,cappos+1,8000))
from(
select *, cappos= patindex('%[^ ]%',item)
from DelimitedSplit8K(@s,'.')
) t
order by ItemNumber
for xml path('') )
,1,1,'')
Find DelimitedSplit8K code here http://www.sqlservercentral.com/articles/72993/