title: Epoxides, cyclic sulfites, and sulfate from natural pentacyclic triterpenoids: theoretical calculations and chemical transformations.
abstract: Several triterpenic derivatives, with the A-ring functionalized, were semisynthesized from oleanolic and maslinic acids. The reactivities of sulfites, sulfate, and epoxides in these triterpene compounds were investigated under different reaction conditions. Moreover, contracted A-ring triterpenes (five-membered rings) were obtained, by different treatments of the sulfate 7. From the epoxide 8, deoxygenated and halohydrin derivatives were semisynthesized with several nucleophiles. Ozonolysis and Beckmann reactions were used to yield 4-aza compounds, from five-membered ring olanediene triterpenes. The X-ray structure of sulfate 7 is given and compared with density functional theory geometries. Theoretical (13)C and (1)H chemical shifts (gauge-invariant atomic orbital method at the B3LYP/6-31G*//B3LYP/6-31G* level) and (3)J(H,H) coupling constants were calculated for compounds 5-9 and 34-36, identifying the (R)- or (S)-sulfur and alpha- or beta-epoxide configurations together with 4-aza or 3-aza structures.
authors.affiliation: Departamento de Química Orgánica, Facultad de Ciencias, Universidad de Granada, 18071-Granada, Spain. agarcia@ugr.es
authors.forename: Andrés
authors.initials: A
authors.lastname: García-Granados
authors.forename: Pilar E
authors.initials: PE
authors.lastname: López
authors.forename: Enrique
authors.initials: E
authors.lastname: Melguizo
authors.forename: Juan N
authors.initials: JN
authors.lastname: Moliz
authors.forename: Andrés
authors.initials: A
authors.lastname: Parra
authors.forename: Yolanda
authors.initials: Y
authors.lastname: Simeó
authors.forename: José A
authors.initials: JA
authors.lastname: Dobado
mesh_terms: D001372:Aza Compounds / Q000737:chemistry*; D018360:Crystallography, X-Ray; D003500:Cyclization; D004852:Epoxy Compounds / Q000737:chemistry*; D008962:Models, Theoretical; D015394:Molecular Structure; D009828:Oleanolic Acid / Q000031:analogs & derivatives / Q000737:chemistry; D013237:Stereoisomerism; D013431:Sulfates / Q000737:chemistry*; D013447:Sulfites / Q000737:chemistry*; D014315:Triterpenes / Q000737:chemistry*
chemical_list: D001372:Aza Compounds; D004852:Epoxy Compounds; D013431:Sulfates; D013447:Sulfites; D014315:Triterpenes; D009828:Oleanolic Acid; C412811:maslinic acid