A One- and Two-Dimensional 1H and 13C N.M.R. Study of Some Lichen Triterpenoids of the Pyxinol Group

Abstract

A complete assignment of the 13C and 1H n.m.r. resonances of the lichen triterpenoids, pyxinol, 3,25-di-O-acetylpyxinol and 3,12,25-tri-O-acetylpyxinol has been achieved by using a combination of one- and two-dimensional n.m.r. data and T1 values. Hydrogen bonding between the 12β- hydroxy group and the carbonyl oxygen of the 25-acetoxy group of 3,25- di-O-acetylpyxinol leads to the furan ring system adopting a� conformation different from that adopted by 25-hydroxy analogues, hence differing chemical shifts are observed for some of the carbons of rings C and D and the furan ring.

New Dammarane Triterpenes from the Aerial Parts of Ibicella lutea Grown in Argentina

“…15 The chemical shift assignments for 9 and 11 were also deduced by comparison with those of their reported epimers at C-20, the acetylated pyxinols. 16 A weak cytotoxic activity (IC 50 ) 5 µg/mL) was found for the 20S*,24S* triol 3 against A-549 (human lung carcinoma) and H-116 (human colon carcinoma) cells, and for the peracetylated derivative 7 against H-116 cells, as well as the diacetylated derivative 10 against A-549 cells. The 20S*,24R* compounds 1 and 2, their derivatives 4 and 6, and the acetylated 20S*,24S* compounds 9 and 11 were devoid of cytotoxic activity: 1, 2, and 4 (IC 50 > 10 µg/mL) against A-549, H-116, and HT-29 (human colon carcinoma) cells, and 6, 9, and 11 (IC 50 > 5 µg/mL) against A-549, H-116, PSN1 (human pancreatic adrenocarcinoma), and T98G (human caucasian glioblastoma) cells.…”

“…Furthermore, the proton and carbon assignments for compound 10 were also made by comparison of its spectroscopic data with those of its reported diasteroisomer, namely, (20 R ,24 R )-20,24-epoxydammarane-3 β ,12 β ,25-trioldiacetate . The chemical shift assignments for 9 and 11 were also deduced by comparison with those of their reported epimers at C-20, the acetylated pyxinols …”

“…Compound 4: colorless prisms; mp 149-150 °C; [R] 26.6 D -12.6°(c 0.075, CHCl3); IR (neat) νmax 3400, 2964, 1454, 1383, 1307, 1085, 994 cm -1 ; 1 H NMR (CDCl3, 200 MHz) δ 3.85 (1H, dd, J ) 8.0, 5.6 Hz, H-24), 3.81 (1H, dd, J ) 4.6, 10.5 Hz, H-1), 3.58 (1H, ddd, J ) 5.0, 10.6, 10.6 Hz, H-12), 3.51 (1H, t, J ) 4.2 Hz, H-3), 2.64 (1H, ddd, J ) 3.8, 3.8, 13.3 Hz, H-11R), 1.24 (3H, s, H-21), 1.23 (3H, s, H-26), 1.07 (3H, s, H-27), 0.97 (3H, s, H-18), 0.90 (3H, s, H-19), 0.90 (3H, s, H-28), 0.89 (3H, s, H-30), 0.80 (3H, s, H-29); 13 C NMR, see Table 2; LREIMS (70 eV) m/z 492 (2), 575 (10), 457 (13), 439 (15), 379 (40), 349 (16), 189 (62), 143 (50), 107 (100), 91 (80), 79 (51); (+)-LRFABMS m/z 515 [M + Na] + (96), 439 (5), 159 (7), 143 (100).…”

“…Compound 6: white powder; mp 218-219 °C; [R] 22 D -7.02°( c 0.035, CHCl3); IR (neat) νmax 2966, 1735, 1465, 1373, 1250 cm -1 ; 1 H NMR (CDCl3, 200 MHz) δ 4.85 (1H, dd, J ) 10.0, 5.0 Hz, H-1), 4.82 (1H, ddd, J ) 10.0, 10.0, 5.0 Hz, H-12), 4.70 (1H, t, J ) 3.0 Hz, H-3), 3.66 (1H, t, J ) 6.5 Hz, H-24), 2.13 (3H, s, OCOCH3), 1.99 (3H, s, OCOCH3), 1.92 (3H, s, OCOCH3), 1.18 (3H, s, H-26), 1.16 (3H, s, H-21), 1.12 (3H, s, H-27), 1.07 (3H, s, H-18), 1.05 (3H, s, H-30),0.98 (3H, s, H-19), 0.92 (3H, s, H-29), 0.85 (3H, s, H-28); 13 C NMR, see Table 2; LREIMS (70 eV) m/z 618 (5), 500 (16) Acetylation of Triol 3 at Room Temperature. Compound 3 (25 mg) was acetylated at room temperature in a similar way to 1 and was purified by HPLC [NP column, 300 × 8 mm, EtOAc-hexane (7:3), flow rate: 1.0 mL] to give 14 mg of 9 (56% yield, R f 0.33 EtOAc-hexane, 7:3) and 6 mg of 10 (24% yield Rf 0.62, EtOAc-hexane, 7:3).…”

“…Acetylation of Triol 3 under Reflux. Compound 3 (25 mg) was acetylated under the same conditions as described for 1, and the product was purified by HPLC as above to give 4 mg of 10 (16% yield, Rf 0.62 EtOAc-hexane, 7:3) and 16 (6), 423 (10), 189 (20), 185 (66), 143 (66), 125 (100).…”