“…The 1 H-NMR spectrum of 4 displayed three methyl singlets at δ 0.99 (3H, CH 3 -14), 1.04 (3H, CH 3 -15) and 2.12 (3H, CH 3 -12); three mutually coupled methylene groups at δ 1.35 (2H, m, CH 2 -2), 1.52 (2H, m, CH 2 -2) and 2.07 (2H, m, CH 2 -2); three olefinic protons at δ 4.53 (1H, br s, H-13a), 4.81 (1H, br s, H-13b) and 5.95 (1H, s, H-10), respectively. In addition, three methine protons at δ 1.59 (1H, d, J = 8.0 Hz, H-6), 2.92 (1H, dd, J = 8.0, 1.9 Hz, H-7) and 3.04 (1H, br s, H-8), along with the 13 C-NMR signals of two sets of carbon-carbon double bond at δ 109.0 (C-13), 115.1 (C-10), 147.7 (C-5) and 157.4 (C-9); two oxymethine carbons of one oxirane ring at δ 59.1 (C-8) and 60.3 (C-7); and one carboxylic acidic carbonyl carbon at δ 171.6 (C-11), evidenced the basic skeleton of 4 as γ-ionylideneacetic acid [ 28 ] with oxirane functionality. The 2 J , 3 J -heteronuclear multiple bond correlation (HMBC) correlations ( Figure 3 ) from CH 3 -14 to C-1, -2, -6; from CH 3 -12 to C-8, -9; from H-6 to C-1, -5, -7; from H-8 to C-7, -9, -10; from H-10 to C-9, -11; and from CH 2 -13 to C-4, -6, respectively, further determined the locations of oxirane and terminal methylene groups to be at C-7/C-8 and C-5.…”