Structures of New Seven-Membered Ring Vibsane-Type Diterpenes Isolated from Leaves of Viburnum awabuki.

Rearranged Vibsane-Type Diterpenes from Viburnum awabuki and Photochemical Reaction of Vibsanin B

“…Routine analyses of 1 H-1 H shift correlated spectroscopy (COSY), 1 H-detected heteronuclear correlation through multiple quantum coherence (HMQC) and 1 H-detected heteronuclear multiple-bond correlation (HMBC) spectra of 1 and 2 implied that both compounds were congeners of neovibsanins A and/or B bearing an E double bond [d 5.86 (ddd,Jϭ15.6,8.8,6. 4 Hz, H-13), 5.59 (d, Jϭ15. 6 Hz,] at the C-13 position, and a hydroperoxyl group at the C-15 position, the presence of which was supported by a low-field C-15 quaternary carbon signal resonated at d 81.7 and a positive KI-starch test.…”

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Vibsane-type diterpenes can be regarded as quite rare natural products because they occur exclusively in Viburnum species such as V. awabuki [1][2][3][4][5][6][7][8][9][10][11] and V. odoratissimum.

12-15)The carbon skeletons of vibsane-type diterpenes consist of three structural subtypes, i.e., 11-and 7-membered ring compounds, and rearranged type (neovibsane-type) such as vibsanins B (12) and C (13), 1,3) and neovibsanin A (14), 2) respectively. Among these three subtypes, neovibsane-type diterpenes occupy a particular position in the vibsane-type natural products, owing to their unprecedented skeleton as well as intriguing biological activities.

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“…Vibsane-type diterpenes can be regarded as quite rare natural products because they occur exclusively in Viburnum species such as V. awabuki [1][2][3][4][5][6][7][8][9][10][11] and V. odoratissimum.…”

Peroxy natural products

“…The leaves of Viburnum awabuki afforded two vibsane hydroperoxides vibsanin K 416 and 18-O-methylvibsanin K 417 as well as their corresponding C-5 epimers 418 and 419, 250,251 of which vibsanin K exhibited significant cytotoxicity against human gastric (NUGC) and oral epidermoid (HONE-1) tumor cells at a concentration of 50 μg/mL. 252 An unusual macrocyclic endoperoxide structure was assigned to neovibsanin C 420 that was obtained from Viburnum aurabuki.…”

Seven-Membered Vibsane-Type Diterpenes with a 5,10-cis Relationship from Viburnum awabuki.

“…This result suggests the occurrence of natural 5-epimers corresponding to the previously reported sevenmembered vibsanins C (6), H (7), K (8), and 18-Omethylvibsanin K (9) and vibanin E (10) with a trans relationship on the C-5 and C-10 positions. 4,5) Herein, we report the isolation and structure of five anticipated isomers, 5-epivibsanin C (1), 5-epi-vibsanin H (2), 5-epi-vibsanin K (3) and 18-O-methyl-5-epi-vibsanin K (4) and 5-epi-vibsanin E (5) from the methanol extract of the leaves of Viburnum awabuki.…”