Synonyms 9,10-Dimethoxy-2-(2,4,6-trimethylphenylimino)-3-(N-carbamoyl-2-aminoethyl)-3,4,6,7-tetrahydro-2H-pyrimido[6,1-a]isoquinolin-4-one
PubChem (CID) 9934746
ChemSpider 8110374 YesY
Chemical and physical data
Formula C26H31N5O4
Molar mass 477.554 g/mol
3D model (Jmol) Interactive image

RPL-554 (LS-193,855) is a drug candidate for respiratory diseases. It is an analog of trequinsin, and like trequinsin, is a dual inhibitor of the phosphodiesterase enzymes PDE-3 and PDE-4.[1] As of October 2015, inhaled RPL-554 delivered via a nebulizer was in development for COPD and had been studied in asthma.[2]

PDE3 inhibitors act as bronchodilators, while PDE4 inhibitors have an anti-inflammatory effect.[1][3]

RPL554 was part of a family of compounds invented by Sir David Jack, former head of R&D for GlaxoSmithKline, and Alexander Oxford, a medicinal chemist; the patents on their work were assigned to Vernalis plc.[4][5]:19-20

In 2005, Rhinopharma Ltd, acquired the rights to the intellectual property from Vernalis.[5]:19-20 Rhinopharma was a startup founded in Vancouver, Canada in 2004 by Michael Walker, Clive Page, and David Saint, to discover and develop drugs for chronic respiratory diseases,[5]:16 and intended to develop RPL-554, delivered with an inhaler, first for allergic rhinitis, then asthma, then for COPD.[5]:16-17 RPL554 was synthesized at Tocris, a contract research organization, under the supervision of Oxford, and was studied in collaboration with Page's lab at King’s College, London.[1] In 2006 Rhinopharma recapitalized and was renamed Verona Pharma plc.[5]


  1. 1 2 3 Boswell-Smith V et al. The pharmacology of two novel long-acting phosphodiesterase 3/4 inhibitors, RPL554 [9,10-dimethoxy-2(2,4,6-trimethylphenylimino)-3-(n-carbamoyl-2-aminoethyl)-3,4,6,7-tetrahydro-2H-pyrimido[6,1-a]isoquinolin-4-one] and RPL565 [6,7-dihydro-2-(2,6-diisopropylphenoxy)-9,10-dimethoxy-4H-pyrimido[6,1-a]isoquinolin-4-one]. J Pharmacol Exp Ther. 2006 Aug;318(2):840-8. PMID 16682455
  2. Nick Paul Taylor for FierceBiotech. October 1, 2015 Verona sets sights on PhIIb after COPD drug comes through early trial
  3. Turner MJ et al. The dual phosphodiesterase 3 and 4 inhibitor RPL554 stimulates CFTR and ciliary beating in primary cultures of bronchial epithelia. Am J Physiol Lung Cell Mol Physiol. 2016 Jan 1;310(1):L59-70. PMID 26545902
  4. see US20040171828, identified in the citations of PMID 16682455
  5. 1 2 3 4 5 ISIS Resources, PLC. August 23, 2006 Proposed Acquisition of Rhinopharma
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