A total of 16 metabolites of bromocriptine could be isolated from rat bile and incubates of rat liver cell preparations using [6-methyl-14C]bromocriptine as substrate. Separation and purification was achieved by reversed-phase liquid chromatography and preparative thin-layer chromatography in conjunction with radioactivity monitoring. Structure elucidation was based on spectroscopic data (UV, IR, NMR, EI- and FD-MS) and the results of amino acid analysis after acid hydrolysis. Based on the identified metabolites four principal transformation process could be described: -Hydrolytic cleavage of the amide bridge leading to the formation of 2-bromolysergic acid amide (3) and 2-bromolysergic acid (7). -epimerization at position 8 of the bromolysergic acid moiety to the iso-derivatives (isobromocriptine, 2-bromo-isolysergic acid (6), its amide (1), etc.) -regiospecific oxidation at position 8' in the proline fragment generating stereoisomeric 8'-hydroxy-bromocriptines (21-24) -further oxidation of the 8'-hydroxylated derivatives by either the introduction of a second hydroxy group at position 9' to give dihydroxylated derivatives (detected as conjugates with glucuronic acid: metabolites 29, 30 and 31), or the opening of the proline ring under formation of the metabolites 4 and 5 containing glutamic acid instead of proline (7', 8'-seco- 8'-carboxy-bromocriptines). It is suggested that the primary and principal metabolic attack occurs at the proline fragment of the drug. In contrast to the biotransformation of ergoline compounds, none of the bromocriptine metabolites detected showed oxidative transformations in the lysergic acid half of the molecule.

The disposition and biotransformation of bromocriptine were investigated in mouse, rat, dog, rhesus monkey and man following administration of the drug substance labelled with either tritium or carbon-14. The enteral absorption of bromocriptine was incomplete and amounted to 30-40% of the dose as estimated directly from the sum of biliary and urinary excretion of radioactive compounds in bile duct cannulated rats and monkeys. The main route of elimination was the bile (80-93% of the absorbed dose). Only 1 to 6% of the radioactive dose was recovered in urine of intact animals and man. Extensive biotransformation of bromocriptine is reflected by very complex metabolite profiles in all tested body fluids and by the almost complete absence of parent drug in urine and bile. Of the numerous drug-derived radioactive components seventeen could be identified. In animals the major urinary metabolites were 2-bromo-lysergic acid (7), its amide (3), and the respective isomers at position 8, metabolites 6 and 1. Bromolysergic acid (7) and bromoisolysergic acid (6) accounted for half of the radioactivity in human urine. In rat and monkey bile up to 40% of the radioactivity was associated with metabolites derived from the oxidation (hydroxylation, ring-opening) of the proline fragment (4, 5, 21-24, 29-31). The hydroxylated compounds were present in the form of conjugates with glucuronic acid. These were subsequently deconjugated in the intestine and recovered in the faeces as the free forms. The presence of the parent drug as a major component in rat plasma following intravenous administration and its absence after oral administration indicated that the elimination of bromocriptine proceeded almost entirely by metabolism in the liver. In vitro studies with isolated rat hepatocytes and 10.000 g supernatant of human liver confirmed the in vivo findings. Based on the structures of the identified metabolites it could be concluded that the biotransformation of bromocriptine in man occurred through the same principal pathways as in all investigated animal species.

890 ml of urine of rats treated with ['4C]205-734 was desalted over an Amberlite XAD-2 adsorption column. The methanol extract dissolved in 10 ml methanol was injected onto an anion exchangecolumn (Nucleosil 10 SB 250 X 1 Omm i.d.) equilibrated in methanol. A gradient of decreasing methanol proportion versus a 0.2 u ammonium hydrogen carbonate buffer eluted a pure glucuronide of 205-734. Its structure was established by NMR, MS, UV, and IRanalyses. This procedure is simple, rapid, andvery selective for the compound of interest.