The First Casbane Hydroperoxides EBC‐304 and EBC‐320 from the Australian Rainforest

Abstract

Investigation of the Australian rainforest plant Croton insularis led to isolation of the first casbane hydroperoxide diterpenes EBC-304 and EBC-320. Extensive DFT and electronic circular dichroism (ECD) calculations in combination with 2D NMR spectroscopy determined the absolute configurations. EBC-304 and EBC-320 both display significant cytotoxicity.

The value of universally available raw NMR data for transparency, reproducibility, and integrity in natural product research

“…EBC-324 ( 42 ) contained an unusually oxidized casbane ( 43 ) ring system, whereas EBC-329 ( 41 ) was the first example of a seco -casbane reported. Some years after a number of additional examples of both the seco -casbane [EBC-328 ( 44 ) and EBC-363 ( 45 )],155 and casbane [EBC-304 ( 46 ) and EBC-320 ( 47 )] series,156 were discovered.…”

New Casbanes and the First trans‐Cyclopropane seco‐Casbane from the Australian Rainforest Plant Croton insularis

“…Recently we reported the absolute configuration determination of two cis ‐cyclopropane casbane hydroperoxides, and other related systems . These studies demonstrated that the B3LYP/6‐31+G** level of theory provides reliable results for comparison of experimental and theoretical electronic circular dichroism (ECD) spectra for the casbane diterpene class.…”

“…The configuration of compounds 6 , 9 – 20 , previously isolated hydroperoxycasbanes EBC‐304 and EBC‐320 and cis ‐cyclopropane seco ‐casbanes EBC‐328 and EBC‐363 are compared in Table . It was found that all cis ‐cyclopropane casbanes and seco ‐casbanes had the 8 R ,9 S configuration and all trans ‐cyclopropane casbanes had the 8 R ,9 R configuration.…”

Alkaloids and Coumarins with Adiponectin-Secretion-Promoting Activities from the Leaves of Orixa japonica

“…The peroxy group containing 15 and 17 might be formed by the single oxygen reaction through natural hydroperoxidation. − However, in the compound isolation process, the peroxide formation could occur due to the solvent choices, isolation method, and sample storage. , Besides these factors, when plants respond to life-threatening changes such as seasonal changes, temperature stress, and invasion of pathogens, they release the hydroperoxide lyase enzyme, which is known to have the capacity to cleave the carbon–carbon double bond. , This makes it difficult to prove that these compounds are natural product compounds or artifacts. However, based on the previous reports on the isolation of naturally occurring peroxycoumarin compounds, − it seems that compounds 15 and 17 may not be artifacts. ,− …”

“…19−21 However, in the compound isolation process, the peroxide formation could occur due to the solvent choices, isolation method, and sample storage. 20,22 Besides these factors, when plants respond to life-threatening changes such as seasonal changes, temperature stress, and invasion of pathogens, they release the hydroperoxide lyase enzyme, which is known to have the capacity to cleave the carbon− carbon double bond. 23,24 This makes it difficult to prove that these compounds are natural product compounds or artifacts.…”