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.

Maslinic Acid-Enriched Diet Decreases Intestinal Tumorigenesis in ApcMin/+ Mice through Transcriptomic and Metabolomic Reprogramming

“…The experimental protocols were approved by the Experimental Animal Ethical Research Committee of the University of Barcelona in accordance with current regulations for animal care and use for experimental purposes. MA was obtained from olive pomace by using the method described by Garcia-Granados et al [8]. The extract used was a white powder comprising 98% maslinic acid and 2% oleanolic acid.…”

Base‐Catalyzed Intramolecular Hydroamination of Cyclohexa‐2,5‐dienes: Insights into the Mechanism through DFT Calculations and Application to the Total Synthesis of epi‐Elwesine

“…It was thus decided to employ the epoxide as an olefin protective group that could then be unmasked later in the synthesis. Epoxide ring opening to form the corresponding iodohydrin, [44] followed by zinc-mediated elimination [45] would thus be used, respectively, to protect then restore the olefinic appendage. Treatment of 29 with a mixture of PPh 3 and I 2 led effectively to epoxide ring opening and formation of the iodohydrin as a mixture of two regioisomers, albeit in 30 % yield.…”

NMR assignment in regioisomeric hydroquinones

“…[16,17] Among the wide range of DFT methods reported in the literature, the O3LYP [18,19] is a GGA hybrid class of functional that has demonstrated to be appropriate in reproducing the NMR properties, not only spin-spin coupling constants [20] but also chemical shifts of carbon, hydrogen and other atoms. [21 -23] In the present study, we report the two-step synthesis of a series of hydroquinones (Scheme 1) that fulfill the key structural features of the parent hydroquinone 1.…”