Do L-sugars (enantiomers of natural sugars) have a sweet taste?
Take a look at tagatose. It is a 6-carbon sugar (a ketohexose like fructose) but is inefficiently metabolized and has about 30% the caloric content of sucrose. It is on the FDA GRAS (generally recognized as safe) list. Unlike common artificial sweeteners, you can cook with it like sugar. It has been industrially produced as a sugar alternative, but it is not clear if it commercially available to consumers at this time.