Mo. Rev. Stat. § 547.090
If any person taking an appeal to the supreme court on conviction for a felony, other than those wherein the defendant shall have been sentenced to suffer death, shall fail to perfect the appeal within six months from the time the appeal is granted, unless good and sufficient cause for not perfecting his appeal be shown to the trial court, for which reason the trial court, or the judge of the trial court in vacation, may extend this time for the period of ninety days, the attorney general may file his motion before the supreme court asking that the appeal may be dismissed or that the judgment of the trial court may be affirmed, whereupon the court shall make an order that the appeal be dismissed, or that the judgment of the trial court be affirmed, as the case may be, unless the defendant shall show to the satisfaction of the court good cause for not perfecting his appeal.
§ 547.090, RSMo