Mo. Rev. Stat. § 474.440: Bond to convey does not revoke devise.

A bond, covenant or agreement made for a valuable consideration, by a testator, to convey any property devised or bequeathed in any last will previously made, does not constitute a revocation of the previous devise or bequest, either in law or equity; but the property passes by the devise or bequest, subject to the same remedies on the bond, covenant or agreement, for specific performance or otherwise, against the devisees or legatees, as might be had by law against the heirs of the testator, or his next of kin, if the same had descended to them.