Naturally Occurring Cembranes

Gas chromatographic/mass spectrometric analysis of cembrenoid diterpenes in kerogen from a lacustrine sediment

“…The characteristic differences in relative ion abundances are apparently governed by the positions of the double bonds. The mass spectrum of cembrene shows the base peak at m/z 93 resulting primarily from the rupture of the 14membered ring by cleavage at positions C(l)/C (14) and C(6)/C(7) and additional loss of the isoprenoid sidechain. Cembrene-A, on the other hand, shows the base peak at m/z 68 resulting from cleavage of the C(13)/ C (14) and C(l)/C(2) bonds.…”

Recent Advances in the Synthesis of α‐Alkylidene‐Substituted δ‐Lactones, γ‐Lactams and δ‐Lactams

“…[5] Both compounds showed significant cytotoxicities against human pharyngeal carcinoma (KB) cells. [5] Later on, some natural compounds containing only α-methylene δ-lactone moieties, such as teucrium lactone (7), [6] crassin (8a) [7] and its acetate 8b [8] or pentalenolactone E (9), [9] were also isolated. Crassin (8a) shows in vitro activity against KB cells and its acetate 8b has antibiotic activity.…”

Synthesis and cytotoxic evaluation of β-alkyl or β-aryl-δ-methyl-α-methylene-δ-lactones. Comparison with the corresponding γ-lactones

“…Representative examples of naturally occurring a-methylene-d-lactones such as: vernolepin (7) [15], vernomenin (8) [15], teucriumlactone (9) [17], crassin (10a) and its acetate 10b [21,22] or pentalenolactone E (11) [16] are depicted in Fig. 1.…”

“…On the other hand, a-methylene-d-lactones 6, although much less abundant in nature [15][16][17][18][19][20][21][22][23], are well known. Representative examples of naturally occurring a-methylene-d-lactones such as: vernolepin (7) [15], vernomenin (8) [15], teucriumlactone (9) [17], crassin (10a) and its acetate 10b [21,22] or pentalenolactone E (11) [16] are depicted in Fig.…”