curl - bash variable subtitution in command until block -

i have trouble short code , can not resolve why it's not working,

r="12345" until $(curl --output /dev/null --silent --head --fail http://www.example.com/$r );     printf '.'     sleep 5 done 

the error near $r in $();.

i have wait end of curl request other stuff.

can please me resolving this?