rpl-554 rpl-554 rpl-554 (ls-193,855) is a drug candidate for respiratory diseases. it is an analog of trequinsin and, like trequinsin, is a highly selective inhibitor of the phosphodiesterase enzyme, pde3; indeed, it is >3000-times more potent against pde3 than pde4. as of october 2015, inhaled rpl-554 delivered via a nebulizer was in development for copd and had been studied in asthma. rpl-554clinical dataother names9,10-dimethoxy-2-(2,4,6-trimethylphenylimino)-3-(n-carbamoyl-2-aminoethyl)-3,4,6,7-tetrahydro-2h-pyrimidoisoquinolin-4-oneidentifiers iupac name n-urea cas number298680-25-8 y e-isomer: 1884461-72-6pubchem cid9934746chemspider8110374 yunii3e3d8t1gixcomptox dashboard (epa)dtxsid00183983 echa infocard100.245.423 chemical and physical dataformulac26h31n5o4molar mass477.565 g·mol−13d model (jsmol)interactive image smiles cc3cc(c)cc(c)c3n=c2cc1-c(cc4oc)c(cc4oc)ccn1c(=o)n2ccnc(n)=o inchi inchi=1s/c26h31n5o4/c1-15-10-16(2)24(17(3)11-15)29-23-14-20-19-13-22(35-5)21(34-4)12-18(19)6-8-30(20)26(33)31(23)9-7-28-25(27)32/h10-14h,6-9h2,1-5h3,(h3,27,28,32)/b29-23+ ykey:csobibxviyaxfm-bynjwebrsa-n y (verify) pde3 inhibitors act as bronchodilators, while pde4 inhibitors have an anti-inflammatory effect. 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.: 19–20 in 2005, rhinopharma ltd, acquired the rights to the intellectual property from vernalis.: 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,: 16 and intended to develop rpl-554, delivered with an inhaler, first for allergic rhinitis, then asthma, then for copd.: 16–17 rpl554 was synthesized at a contract research organization, under the supervision of oxford, and was studied in collaboration with page's lab at king’s college, london. in 2006 rhinopharma recapitalized and was renamed verona pharma plc.