Step 1Combine the sugar, water and vanilla bean in a small saucepan. Boil 5 minutes. (The syrup can be made 1 week ahead and refrigerated. Remove the vanilla bean before using.)
Step 2Put the syrup, prunes, Port, red wine and zest in a nonaluminum saucepan. Bring to boil, then reduce the heat to a simmer; cook, uncovered, 2 minutes. Transfer to a bowl to cool.
Step 3Cover airtight; refrigerate for at least 2 days or up to 2 weeks. Serve chilled.