Drain the water chestnuts, discarding the soy sauce. Place a pineapple chunk in the center of each piece of bacon, then place a water chestnut on top of that. Fold the ends of the bacon over the water chestnut, and secure with a toothpick. Repeat with the remaining bacon, pineapple, and water chestnuts. Gently toss the bacon-wrapped chestnuts with brown sugar in a bowl, then place onto the prepared baking sheet.