While doing a search for this, I came upon something interesting.. I know it was Rhodium and someone i think it was Madmax discussing in an earlier thread the mechanism of GBL -> GHB transformation in the stomach.. Well, while searching for something related to this compound, I found a site that sells a product thats converted to GHV in the stomach by the same mechanism GBL is to GHB.. from the site:
Upon ingestion, Tranquili-G is converted via lactonase catalyzed
hydrolysis -- the same mechanism by which GBL is converted to GHB (1) -- to the potent GHB analogue, 4-methyl-GHB (see *).
4-methyl-GHB has been found to bind to the GHB receptor with 15% GREATER affinity than GHB itself (2). Gamma-hydroxybutyrate
exerts its effects through specific GHB receptors (3), thus consumption of a precursor to a compound which binds to the GHB receptor
would be expected to result in physiological and psychological effects quite similar to those produced by GHB, such as sedation,
reduction of anxiety, and stimulation of growth hormone release.
Also, here's a little more info on GHV:
http://www.erowid.org/chemicals/ghv