Under applicable law, as understood by the court, if a compound on which a patent is sought is very similar in structure to a known compound, as 3,4-DCPA and 3,4-DCAA were, a rebuttable presumption arises that the later compound is obvious from the earlier one. "To rebut this presumption it must be shown 'that the claimed compound possesse[d] unobvious or unexpected beneficial properties not actually possessed by the prior art homologue.'"[7]