Crystal structures of crotocembraneic acid and neocrotocembraneic acid

Department of Chemistry Faculty of Science, Chulalongkorn University* Department of Physics, Faculty of Science and Technology, Thammasat University, Bangkok, Thailand.**
○Wilaiwon Tirawanich* Thapong Teerawatananond* Narongsak Chaichit** Amorn Petsom*

Two cembranoids, crotocembraneic acid, (1E,3E,7E,11Z)-1-isopropyl-4,8-dimethylcyclotetradeca-1,3,7,11-tetraene-12-carboxylic acid (1) and neocrotocembraneic acid, (1E,3E,7E,11E)-1-isopropyl-4,8-dimethylcyclotetradeca-1,3,7,11-tetraene-12-carboxylic acid (2), C20H30O2, were isolated from Croton oblongifolius Roxb. which had been used as Thai traditional medicine to treat human gastrointestinal track. In this work, we revealed their differences in Z- and E- molecular configurations by X-ray analysis. Cembranoids 1 and 2 were crystallized in space groups monoclinic P21/a and triclinic P(1) with their unit cell parameters a=9.8513(5)Å, b=10.5630(10)Å, c=18.5873(11)Å, β=102.136(2)゚ and α=7.64120(10)Å, b=9.7269(2)Å, c=13.11200(10)Å, α=95.387(0)゚, β=98.222(1)゚, γ=98.899(1)゚. Dihedral angles C10-C11-C12-C13 of 1 and 2 were -175.24(0.30)゚ and -2.08(0.30)゚, respectively. Both stereoisomers formed a pair of inter-molecular hydrogen bonding between the hydroxyl and carbonyl groups. The crystal packing of 1 showed the O2H…O1 hydrogen bond distance of 2.626(3)Å, which was slightly shorter than a hydrogen bond of 2.6433(19)Å in molecular crystal 2.


[1] Roengsumran S., Achayindee S., Petsom A., Pudhom K., Singtothong P., Surachetapan C., Vilaivan T., Two new cembranoids from Croton oblongifolius, J. Nat. Prod., 61, (1998), 652-654.