Chem2Cure Research and Therapeutics
Donate Start here

Domperidone Motilium

A prokinetic and anti-sickness medicine for nausea, vomiting and slow gastric emptying. It barely crosses the blood-brain barrier, so it avoids the movement disorders that metoclopramide can cause. Sold over the counter across much of Asia and Europe, including Bangladesh, but it has carried warnings since 2012 for cardiac arrhythmia at doses above 30 mg a day and in people over 60, and it was never approved for sale in the United States.

  • Peripheral dopamine D₂/D₃ receptor antagonist
  • Marketed from 1979; never approved in the US
  • C22H24ClN5O2 · 425.91 g/mol
  • CAS 57808-66-9

Convergent route through two benzimidazolones

7 stages · two halves joined at the end

Cut domperidone at the two carbon-nitrogen bonds either side of the piperidine nitrogen and it falls into two benzimidazolones of almost the same kind: one carrying a three-carbon chain with a halide at the end, the other carrying the piperidine ring and a chlorine on the benzene ring. Both halves are built the same way, by making the benzimidazolone ring and then attaching what has to hang off its nitrogen, and the last step simply alkylates the piperidine nitrogen of the second half with the halide of the first. The difficulty is in the first half, and it is a selectivity problem rather than a reactivity one: benzimidazolone has two chemically identical N-H groups, so alkylating one of them and not both is the whole game. The route shown here solves that by building a protecting group into the ring-forming step itself, using ethyl acetoacetate so that cyclisation and mono-protection happen at once.

Scale: laboratory and patent scale, as collected in the review

o-Phenylenediamine (benzene-1,2-diamine)
+
Ethyl acetoacetate
Step 1 91% isolated
KOH, 110 °C, 10 h
no separate protecting-group step
the ring is made and half-protected in one operation · ethyl acetoacetate condenses, cyclises and rearranges, leaving an isopropenyl group on one of the two nitrogens, so the other is the only one left to alkylate
N-Isopropenyl-2-benzimidazolone no public CAS
N-Isopropenyl-2-benzimidazolone no public CAS
+
1-Bromo-3-chloropropane
Step 2 92% isolated
1-bromo-3-chloropropane, 10% KOH (aq)
TBAB as phase-transfer catalyst, 25 °C, 8 h
alkylation of the one free nitrogen · the reaction is two-phase, so tetrabutylammonium bromide ferries the deprotonated benzimidazolone into the organic layer to meet the dihalide · the bromide end reacts and the chloride end is left for later
1-(3-Chloropropyl)-3-isopropenyl-2-benzimidazolone no public CAS
1-(3-Chloropropyl)-3-isopropenyl-2-benzimidazolone no public CAS
Step 3 90% isolated
HCl (1 mol/L), room temperature, 5–6 h
hydrolysis, no metal and no hydrogenation
the isopropenyl group comes off as acetone on hydrolysis · 90% yield at 99.1% purity, and the three steps together avoid ever having to separate a mono- from a di-alkylated product
Intermediate 1: 1-(3-chloropropyl)-2-benzimidazolone no public CAS
1,4-Dichloro-2-nitrobenzene
+
tert-Butyl 4-aminopiperidine-1-carboxylate (N-Boc-4-aminopiperidine)
Step 4
weak base, N-protected 4-aminopiperidine
Boc shown; benzyl, Cbz or ethoxycarbonyl all used
the second half starts from the other end · the chlorine ortho to the nitro group is the activated one, so the amine displaces it and leaves the para chlorine in place, which is the chlorine that ends up on the finished drug
N-(4-Chloro-2-nitrophenyl)-N-Boc-piperidin-4-amine no public CAS
N-(4-Chloro-2-nitrophenyl)-N-Boc-piperidin-4-amine no public CAS
Step 5
RANEY®-Ni with N₂H₄·H₂O, or 5% Pd/C with N₂H₄ in MeOH
transfer hydrogenation rather than H₂ gas
nitro to amine, and the choice of method follows the protecting group · hydrazine donates the protons, which keeps the Boc group intact where hydrogenolysis would threaten a benzyl one · nitro reduction runs through nitroso, hydroxylamine, azoxy and azo species, so the catalyst has to take every one of them all the way down to the amine
N-(2-Amino-4-chlorophenyl)-N-Boc-piperidin-4-amine no public CAS
N-(2-Amino-4-chlorophenyl)-N-Boc-piperidin-4-amine no public CAS
Step 6
carbonyl reagent (urea, CDI or CO₂), then TFA (20–35%), rt
ring closure, then the Boc group off
the same cyclisation as the first half, on a different diamine · urea with 1,2-diaminobenzene has been reported at 98% without any catalyst, and CO₂ does the same job with water as the only by-product, which is the greener option the review argues for
Intermediate 2: 5-chloro-1-(piperidin-4-yl)-2-benzimidazolone no public CAS
Intermediate 1: 1-(3-chloropropyl)-2-benzimidazolone no public CAS
+
Intermediate 2: 5-chloro-1-(piperidin-4-yl)-2-benzimidazolone no public CAS
Step 7
alkali, KI as catalyst
isolated by column or by pH adjustment
the two halves meet · the piperidine nitrogen displaces the chloride, with iodide swapping in first to make a better leaving group · the same alkylation chemistry as step 2, which is why this route needs only one kind of reaction done well
Domperidone (Motilium)
75% intermediate 1, overall vs 83% in one step 99.1% purity of intermediate 1 vs not reported blocked di-alkylated by-product vs the main loss none added protecting group steps vs two (Boc on, Boc off)

The one-step comparison is the direct alkylation of unprotected benzimidazolone with 1-bromo-3-chloropropane in 10% NaOH and dichloromethane, reported at 83% in a patent, where the review notes the di-substituted by-product is not discussed. The route below reaches a lower overall yield across three steps but with the selectivity problem designed out rather than tolerated.

Yu, L.; Shao, R.; Guo, Q.; Hong, H.; Zhu, N.
The methodology for preparing domperidone: strategies, routes and reaction processes
RSC Adv. 2022, 12, 22869–22880 · Schemes 1, 5, 8 and 10, Table 1

Open the paper · DOI 10.1039/D2RA03777G Free to read under CC BY-NC 4.0, which allows non-commercial reuse

Background on the chemistry

Why the benzimidazolone ring is usually closed with urea or carbon dioxide rather than phosgene. The review traces nearly every carbonyl reagent in use back to carbon monoxide, which is toxic, explosive and energy-expensive to make, and argues that CO₂ is the obvious replacement for this particular ring: it reacts with o-phenylenediamine to give the benzimidazolone with water as the only by-product. The same paper, read for a different reason.

Yu, L.; Shao, R.; Guo, Q.; Hong, H.; Zhu, N.
The methodology for preparing domperidone: strategies, routes and reaction processes
RSC Adv. 2022, 12, 22869–22880 · Figures 2 and 3

Open the paper · DOI 10.1039/D2RA03777G Free to read under CC BY-NC 4.0

All drugs