Studies on rearrangements in derivatives of grandiflorenic acid. Part 1. Reaction of the epoxides of methyl (–)-kaur-9(11)-en-19-oate and (–)-kaur-9(11)-en-19-oic acid with boron trifluoride-diethyl ether either in the absence or in the presence of N-nitrosomethylurea. Formation of two diterpenes of a new skeletal type

Abstract

~~ ~~On treatment with boron trifluoride-diethyl ether in benzene the epoxide (3b) of methyl (-) -kaur-9( 11 )en-19-oate (2c) yielded an aldehyde (5a). During the epoxidation of compound (2c) with mchloroperbenzoic acid it was observed that in the presence of N-nitrosomethylurea the expected epoxide (3b) was not obtained, but instead compound (4) was isolated. Detailed studies showed that epoxide (3b) is an intermediate for the formation of compound (4) from compound (2c), and aldehyde (5a) is also involved in its mechanistic pathway. Epoxidation of aldehyde (5a), followed by acid treatment, led to compound (4). On rupture with boron trifluoride-diethyl ether in acetic anhydride epoxide (3b) afforded acylal (5b) in good yield.(-) -Kaur-9( 1 1 ) -en-1 9-oic acid (2b) behaved similarly. On rupture with boron trifluoride-diethyl ether its epoxide (3a) gave also an aldehyde, (5c), while on treatment with boron trifluoride-diethyl ether in acetic anhydride it yielded acylal (5d).

Cytostatic and Cytotoxic Activity of Synthetic Diterpene Derivatives Obtained from (-)-Kaur-9(11), 16-Dien-19-Oic Acid Against Human Cancer Cell Lines

“…All these compounds (1), (2), (3), (4a), (4b), (5), and (6) had physical and spectroscopic data identical to those reported by Nakano and co-worker [1,2,3].…”

“…The compound (5) has been converted into the new ring system compounds (1) and (2) via epoxidation and rearrangement; refer to Schemes 2 and 3. The synthetic approach used by Nakano and co-worker [1] was taken.…”

Synthetic diterpene derivatives from kaura-9(11),16-dien-19-oic acid: Cytostatic and cytotoxic activity against human cancer cell lines

“…Compounds 1, 2, 3, 4a, 4b, 5, and 6 were prepared according to a procedure previously described by Nakano et al [1]. Testing against human cancer cell lines.…”

“…In this context, a series of modifications were performed (Scheme 1) on the molecule of grandiflorenic acid or (-)-kaura-9(11),16-dien-19-oic acid (compound 7) as starting material, which was obtained from the Venezuelan species of espeletia using the synthetic approach developed by Nakano et al [1].…”

Skeletal Rearrangements of Rings C and D of the Kaurene and Beyerene Tetracyclic Diterpenoids

“…46 However, the reactions of the 9α,11α-epoxide and the 9α,11α-diol 39 derived from the methyl ester of 16,17-dihydrograndiflorenic acid were more complex. [47][48][49] They involved migration of the C-8:C-15 bond to C-9 and a fragmentation reaction of ring C to form an aldehyde 41. This aldehyde derived from the original C-11 alcohol could be trapped as a cyclic enol ether by further epoxidation of the C-8:C-9 double bond.…”