Synthesis and absolute stereochemistry of (-)-protolichesterinic acid, antitumor antibiotic lactone from Cetraria islandica

Brasilane sesquiterpenoids and alkane derivatives from cultures of the basidiomycete Coltricia sideroides

“…Preliminary analyses of 1 H-1 H COSY and HMBC data (Fig. 1) suggested that compound 1 should be a brasilane-type sesquiterpenoid glycoside [15]. The double bond was located between C-5 and C-10 as supported by HMBC correlations from δ H 1.84 (3H, s, H-12) to δ C 124.6 (s, C-10) and from δ H 2.44 (1H, d, J = 13.7 Hz, H-4a), 1.62 (1H, d, J = 13.7 Hz, H-4b) and δ H 2.04 (1H, m, H-6) to δ C 140.4 (s, C-5).…”

“…The molecular formula was established to be C 15 2 , 238.1933). The 13 C NMR spectrum displayed fifteen carbon resonances with similarities to those data of the aglycone in compound 1 (Table 1) except that the methyl of C-15 in 1 was oxygenated into an oxymethylene (δ C 65.4, t) in 2, as supported by the HMBC correlation from δ H 3.61 (1H, dd, J = 10.5, 6.5 Hz, H-15a) and 3.33 (1H, dd, J = 10.5, 7.3 Hz, H-15b) to δ C 40.1 (d, C-9).…”

“…Compound 3 was isolated as a colorless oil, possessing a molecular formula C 15 2 , 238.1933). On the basis of extensive 2D NMR data analysis, we established that compound 3 was a derivative of compound 2.…”

[1,3]‐Transfer of Chirality during the Nicholas Reaction in γ‐Benzyloxy Propargylic Alcohols

“…Although the relative stereochemistry was established by NOE studies, we prepared the alternative trans-lactone 22 from 21 to avoid any misinterpretation arising from conformational fluctuation of the five-membered ring. [27] Alkylation of 21 under the usual basic conditions provided the expected trans-lactone 22 as the major product. [28] Comparative NOE studies permitted us to establish unambiguously that the g-butyrolactones obtained from the reduced acetylene have the cis relative stereochemistry.…”

“…The combined organic phases were washed with saturated aqueous NaCl, dried (MgSO 4 ), filtered, and concentrated to afford the lactone 20 a as a white solid (50.7 mg, 72 % yield General procedure for the preparation of trans-a,g-disubstituted butyrolactones: preparation of (3 S,5 S)-3-methyl-5-tridecyldihydrofuran-2-one (22): nBuLi (0.21 mL of a 1.9 m solution in hexane, 0.39 mmol) was slowly added to a solution of diisopropylamine (64 mL, 0.44 mmol) in THF/HMPA (4:1) (3 mL) at À78 8C under argon. The mixture was stirred for 15 min and then a solution of the lactone 21 [40] (100 mg, 0.37 mmol) in THF/HMPA (4:1) (0.5 mL) was added dropwise. The resulting mixture was stirred for 20 min at À78 8C, whereupon a solution of MeI (24 mL, 0.44 mmol) in THF/HMPA (4:1) (0.5 mL) was added.…”