Which of the following correctly revises the sentence for grammar and clarity?

A) Although the hydrocarbon calicene has so far defied synthesis, it has been estimated that it would have a dipole moment as large as 5.6 d.
B) Although the hydrocarbon calicene has so far defied synthesis, it has been estimated to have a dipole moment as large as 5.6 d.
C) The hydrocarbon calicene, although it has so far defied synthesis, but it has been estimated that it would have a dipole moment as large as 5.6 d.
D) Despite the hydrocarbon calicene's synthesis being elusive so far, it has been estimated to have a dipole moment as large as 5.6 d.