Quinagolide Explained

Quinagolide, sold under the brand name Norprolac, is a selective dopamine D₂ receptor agonist which is used to reduce elevated levels of prolactin (hyperprolactinemia).^[1] It has also been found to be effective in the treatment of breast pain.^[2] It is used in the UK, but it is not available in US.

Chemistry

Quinagolide is a racemate composed of the following two enantiomers:^[3]

Synthesis

Laboratory synthesis

The first synthesis of quinagolide was disclosed in patents filed by Sandoz.^[4]

A sequence of nine steps is required to transform the starting material 5-methoxy-2-tetralone (1) into the octahydrobenzo[g]quinoline ring system with the correct stereochemistry required. This intermediate (11) is then converted in another five steps to the drug. Transformation of the ester (13) into the amine (15) is accomplished by a Curtius rearrangement in which an acyl hydrazide is treated with nitrosyl chloride.^{[4] [5] [6]}

Manufacture

The laboratory route was not practical for the synthesis of quinagoline on a large scale. Therefore scientists at Novartis developed an improved process.^[7]

The starting material is 1,6-dimethoxynaphthalene (1). This is selectively lithiated at the C-7 position and reacts with (2Z)-ethyl 2-cyano-3-ethoxyacrylate (2), to give the cyanoacrylate (3). Catalytic hydrogenation and hydrolysis produces (5). Birch reduction of (5) leads first to (6) which on acid work-up gives the imine (7), which is reduced with sodium borohydride to yield (8). Fischer esterification with methanol gives an ester that is next alkylated with 1-iodopropane to give (11). The required stereochemistry for quinagoline is set in the final steps.^{[7] [8] [9]}

Notes and References

1. Di Sarno A, Landi ML, Marzullo P, Di Somma C, Pivonello R, Cerbone G, Lombardi G, Colao A . 6 . The effect of quinagolide and cabergoline, two selective dopamine receptor type 2 agonists, in the treatment of prolactinomas . Clinical Endocrinology . 53 . 1 . 53–60 . July 2000 . 10931080 . 10.1046/j.1365-2265.2000.01016.x . 31677949 .
2. Book: Pluchinotta AM . The Outpatient Breast Clinic: Aiming at Best Practice . 20 April 2015 . Springer . 978-3-319-15907-2 . 167– .
3. Book: Rote Liste Service GmbH (Hrsg.) . Rote Liste 2017 - Arzneimittelverzeichnis für Deutschland (einschließlich EU-Zulassungen und bestimmter Medizinprodukte) . Red List 2017 - List of medicinal products for Germany (including EU approvals and certain medical devices) . German . Rote Liste Service GmbH . Frankfurt/Main . 2017 . 57th . 978-3-946057-10-9 . 214 .
4. EP . 0077754 . Nordmann R, Petcher TJ . Novel pharmaceutically active 1,2,3,4,4a,5,10,10a-octahydrobenzo(g)quinoline derivatives . patent . 1983-04-27 . 1982-10-06 . 1981-10-16 . Sandoz.
5. Nordmann R, Petcher TJ . Octahydrobenzo[g]quinolines: potent dopamine agonists which show the relationship between ergolines and apomorphine . Journal of Medicinal Chemistry . 28 . 3 . 367–375 . March 1985 . 3973904 . 10.1021/jm00381a017 .
6. Web site: Quinagolide . Thieme . 2024-07-07.
7. 10.1021/op0000531 . Practical and Large-Scale Synthesis of rac-(3 S,4a R,10a R)- 6-Methoxy-1-propyl-1,2,3,4,4a,5,10,10a-octahydrobenzo[g]quinoline-3-carboxylic Acid Methyl Ester . 2000 . Bänziger M, Cercus J, Stampfer W, Sunay U . Organic Process Research & Development . 4 . 6 . 460–466 .
8. Comparini LM, Menichetti A, Favero L, Di Pietro S, Badalassi F, Ryberg P, Pineschi M . Development of an asymmetric formal synthesis of (-)-quinagolide via enzymatic resolution and stereoselective iminium ion reduction . Organic & Biomolecular Chemistry . 21 . 31 . 6389–6396 . August 2023 . 37492953 . 10.1039/D3OB00946G .
9. Chavan SP, Kadam AL, Kawale SA . Total Synthesis of (±)-Quinagolide: A Potent D₂ Receptor Agonist for the Treatment of Hyperprolactinemia . ACS Omega . 4 . 5 . 8231–8238 . May 2019 . 31459911 . 6648496 . 10.1021/acsomega.9b00903 .