exclude atom from being matched (multiple letters)

Can sed negate matching an atom, i.e. multiple letters?

Example: match any line starting with foo, but NOT ending with a dot 
followd by zero or more spaces

(end of line marked with $)

foo rhabarber etc .$
foo rhabarber etc .    $
foo rhabarber etc$
foo rhabarber etc     $


only match third and forth line.

atom is:
(\. *)

negate atom???
sed '/foo.*^(\. *)$/  # does not work, of course, matches beginning of line