Structures of Us-7 and Us-8: a new type of oxindole alkaloids isolated from Uncaria attenuata Korth

Medicinal uses, phytochemistry and pharmacology of the genus Uncaria

“…Based on the detailed information on indole alkaloids given by nuclear magnetic resonance (NMR) spectroscopy, we can confirm their stereo-chemistry. For instance, the configuration of H-15 is most likely to be α-orientation (Aimi et al, 1997). On the basis of the correlations of H-15 with H-3 and H-20 in the NOESY spectrum ascertain the configuration of C-3 and C-20.…”

“…The presence of β-methoxyacrylic ester can be identified by characteristic nuclear magnetic resonance (NMR) signals, such as the 1 H-NMR signals at -CO 2 CH 3 (δ $3.62, 3H, s), OCH 3 (δ $ 3.78, 3H, s) and H-17 (δ $ 8.20, 1H, s) (Aimi, 1997) and the 13 C-NMR signals at C-16 (δ $ 111.8), C-17 (δ $ 160.7), OCH 3 (δ $ 61.2) and COOCH 3 (δ $169.6 and 51.2 each) (Ernest. et al, 1974).…”

Chemistry of Indole Alkaloids Related to the Corynanthe-Type from Uncaria, Nauclea and Mitragyna Plants

“…With requisite substrate 20 for the radical cyclization in hand, we turned our attention to the construction of the Corynantheoid skeleton. Radical cyclization of vinyl iodide (20) using n-Bu 3 SnH and Et 3 B in toluene at room temperature afforded the desired tetracyclic product (21) possessing the C3/C15 cisrelationship as the major product in 33% yield, along with 19(Z) isomer (23) (17% yield), and two indoline derivatives (25 and 27) (32% total yield). The use of Ph 3 SnH in place of n-Bu 3 SnH slightly improved the product ratio of 21 to 23 to 2.5:1 (44% total yield).…”

“…Along with the C-seco Corynanthe-type oxindole alkaloid (30) described above, a new class of alkaloids, Us-7 (31) and Us-8 (32), were isolated [21]. Their novel structures, which are the first examples of D-seco Corynanthe-type indole alkaloids, were elucidated by spectroscopic analyses and biogenetic consideration.…”

“…A new alkaloid having a hydroxyl group at C14 in the heteroyohimbine skeleton was isolated and its structure established by partial synthesis [19]. We investigated the constituents of the stem bark and hooks of this plant in collaboration with phytochemists from Chulalongkorn University and found new types of oxindole alkaloids, i.e., salacin (29) [20], 3-oxo-7-hydroxy-3,7-secorhynchophylline (30) [20], Us-7 (31), and Us-8 (32) [21]. Their structures were initially inferred from the results of spectroscopic analyses and then determined by asymmetric total synthesis or chemical transformation from known natural products, as follows.…”