Abstract: The disclosure provides new compounds and compositions thereof, and methods for treating or ameliorating a disorder relating to CDG-Ia. In particular, the disclosure provides benzoisothiazolone inhibitors of PMI, which have been synthesized and their ability to drive glycosylation has been demonstrated. The disclosure provides two synthetic routes for these compounds, including a new copper-catalyzed N-arylation reaction amenable to parallel derivitization. The disclosed compounds represent potent inhibitors of PMI, and their dose-dependent efficacy in cell-based models of glycosylation have been demonstrated. In addition, the disclosed compounds are selective over PMM and therefore, are useful in treating or ameliorating a disorder relating to CDG-Ia.