progesterone carboxymethyloxime progesterone carboxymethyloxime progesterone carboxymethyloxime, or progesterone 3-(o-carboxymethyl)oxime (p4-3-cmo), is a progestin which was never marketed. it is an oral prodrug of progesterone with improved pharmacokinetic properties. the compound was developed in an attempt to address the poor oral pharmacokinetics of progesterone, including its very low bioavailability and short biological half-life. these properties of progesterone are thought to be caused by its low water solubility and high metabolic clearance rate due to rapid degradation in the intestines and liver. drugs with low aqueous solubility are not absorbed well in the intestines because their dissolution in water is limited. progesterone carboxymethyloximeclinical dataother namesp4-3-cmo; progesterone 3-carboxymethyloxime; progesterone 3-(o-carboxymethyl)oxime; 3-(o-carboxymethyl-oximino)progesterone; oxy]acetic acidroutes ofadministrationby mouthdrug classprogestogen; neurosteroididentifiers iupac name 2-phenanthren-3-ylidene]amino]oxyacetic acid cas number50909-89-2 118860-31-4 (potassium)pubchem cid11977776chemspider10151119chebichebi:62042echa infocard100.164.875 chemical and physical dataformulac23h33no4molar mass387.520 g·mol−13d model (jsmol)interactive image smiles cc(=o)1cc21(cc32ccc4=c/c(=n/occ(=o)o)/cc34c)c inchi inchi=1s/c23h33no4/c1-14(25)18-6-7-19-17-5-4-15-12-16(24-28-13-21(26)27)8-10-22(15,2)20(17)9-11-23(18,19)3/h12,17-20h,4-11,13h2,1-3h3,(h,26,27)/b24-16+/t17-,18+,19-,20-,22-,23+/m0/s1key:ppelyuttzhliaz-cdudaxdssa-n p4-3-cmo (as the potassium salt) showed water solubility that was increased by more than four orders of magnitude relative to progesterone (solubility = 9.44 mol/l and 0.0006 mol/l, respectively). in addition, it showed an in vitro terminal half-life in rat liver microsomes that was 363-fold longer than that of progesterone (half-life = 795.5 minutes and 2.2 minutes, respectively). as such, p4-3-cmo could have both improved absorption and increased metabolic stability relative to progesterone. however, the compound has not been further assessed nor studied in humans.