Short total syntheses of both the putative and actual structures of the clerodane diterpenoid (+/-)-sacacarin by double annulation.
[reaction: see text] The putative structure of the naturally occurring clerodane diterpenoid (+/-)-sacacarin has been prepared in only 10 steps, six of which are C-C bond-forming steps, in a chemo-, regio-, and diastereoselective manner. The key part of the synthesis is the double annulation (double Michael, Pinner, and Dieckmann reaction) of a tethered carbon diacid and 3-butyn-2-one. A corrected structure for sacacarin is proposed, and the structure is proven by synthesis.
Clerodane Diterpenoid Glucosides from the Stems of Tinospora sinensis.
Ten new clerodane diterpenoid glucosides (1-10) and three known analogues (11-13) were isolated from an EtOAc extract of the stems of Tinospora sinensis. Spectroscopic analyses and chemical methods were used to elucidate the structures of these isolates. The absolute configurations of tinosinenosides A-C (1-3) were established by using experimental and calculated ECD data. Their cytotoxicity against the human epithelioid cervical carcinoma (HeLa) cell line and the nitric oxide production inhibitory activity of lipopolysaccharide-activated N9 microglial cells were tested. 1-Deacetyltinosposide A (12) exhibited mild cytotoxicity against HeLa cells, with an IC50 value of 8.35 ± 0.60 μM.
Biologically active clerodane-type diterpene alcohol and its glycosides from the root-stalks of ferns
A diterpene alcohol showing a growth inhibition of lettuce was isolated from the root-stalks of Dicranopteris pedata and Gleichenia japonica. Its structure was determined to be (6S,13S)-cleroda-3,14-diene-6,13-diol 1, an aglycone of the two glycosides previously isolated from G. japonica; the chirality at both C-6 and C-13 was assigned as S by application of the β-D-glucosylation-shift rule and by measurement of 13C NMR chemical shifts, respectively. Further, two glycosides showing growth inhibition were also isolated from D. pedata and they were characterised as the 13-O-β-L-fucopyranosyl-(1 → 2)-α-L-rhamnopyranoside 3 and 13-O-α-L-fuoopyranosyl-(1 → 2)-[α-L-rhamnopyranosyl-(1 → 3)]-α-L-rhamnopyranoside 4 of the diterpene alcohol; the above assignment of the chirality at C-13 was established by measurement of nuclear Overhauser enhancement for the trisaccharide. In addition, a glycoside showing growth acceleration was also isolated and its structure was determined to be (6S,13S)-13-O-β-L-fucopyranosyl-6-O-α-L-rhamnopyranosylcleroda-3,14-diene-6,13-diol 2.