I'm not sure if this stuff qualifies for 'psychoactive', but might still be of interest for some bees. I got the following from the second of two books called 'Pharmaceutical Manufacturing Encyclopedia' by Marshall Sittig, Noyes Publications:
Manufacturing Process:
A charge of 1,000 g of ground velvet beans was extracted with 9 liters 1% aqueous acetic acid at room temperature over a 20-hour period with occasional stirring during the first 4 hours. The liqour was decanted and the bean pulp slurry was vacuum filtered through a cake of acid-washed diatomaceous earth in a Buechner funnel. The decanted liquor was combined with the filtrate and concentrated under vacuum and a nitrogen atmosphere to a volume of 900 ml. After treating with acid-washed activated carbon, the concentrate was then filtered through acid-washed diatomaceous earth.
After concentrating the filtrate to approximatelly 400 ml, solids started crystallizing out at which time the filtrate was cooled by refrigerating at 5 °C for several hours. Filtration gave 18.7 g, mp 284 ° to 286 °C (dec.); [a]D 8.81 ° (1 % solution in aqueous 4 % HCl). The infrared spectrum and paper chromatography indicated very good L-Dopa according to U.S. Patent 3,253,023
Various synthetic routes are also described by Kleeman & Engel
