Ana Moore

Sesquiterpenes of nine european liverworts from the genera, Anastrepta, bazzania, jungermannia, lepidozia and Scapania

Abstract The essential oils of fourteen liverwort specimens from nine species of the Jungermanniales have been examined as to their sesquiterpenes. The barbatenes prove to be present in detectable amounts in all but one species. Bazzanene is frequently found with the barbatenes and new chemical evidence does not support the previously assigned structure but is consistent with a structure diastereomeric to trichodiene. This is consistent with a biogenetic rationale for the barbatene skeleton. Anasterptene, a novel crystalline tetracyclic hydrocarbon, has been found in numerous oils, and chemical degradation established a common skeleton with myliol. The samples of genus Scapania elaborate sesquiterpenes of the enantiomeric humulene-longifolene sequence. New members of this group found are (−)-β-longipinene, (−)-longipipanol, and (+)-γ-himachalene. The related germacrene series is represented by a cadinene, (−)-α-ylangene, and (−)-sativene. A series of cis-fused selinenes have also been found, which are more closely allied to the germacrene-sativene group than to typical trans-fused selinenes. One of these selinenes is shown to be the same as the material previously designated as sibirene. Scapania undulata also elaborates (+)-α- and β-chamigrene, and a number of novel hydrocarbons of still unknown structure.

Anastreptene, a commonly encountered sesquiterpene of liverworts (hepaticae)

Abstract Anastreptene ( 9b ), a tetracyclic mono-ene of the same skeleton as myliol ( 10 ) has been found as a common constituent of essential oils derived from liverworts. The relationship to myliol is established by spectral comparison between the hydroboration products and the related ketones from anstreptene and myliol degradation products. The additional degradative chemistry for anastreptene could not be rationalized based on the original myliol assignment ( 4 ), but accord with the recent revision based on X-ray crystallography and provide a confirmation of the stereochemical assignments for myliol and anastreptene.

The structure of isobarbatene, the stable tricyclic end-point of the bazzanene-barbatene sesquiterpenes

Abstract The barbatenes (e.g. 3) and a number of other sesquiterpenes afford a novel rearrangement product on treatment with CF3CO2H. This substance, designated isobarbatene, is shown to have structure 6, the result of a bicyclo-[3.2.1]→[2.2.2]→[3.2.1] rearrangement followed by an exo Me shift and deprotonation. The structure assignment is based on spectral and chiroptical data for olefin 6 and its degradation products 8,9 and 10.

Acetyl Cation Facilitated Cyclizations of Olefinic Aldehydes. III.1 Factors Determining Regiochemistry in Acroleins

Abstract Recent reports3,4 of the use of Ac2O-HClO4-EtOAc as a reagent for the cyclizations of olefinic carbonyl compounds in other laboratories contrast with our experience with the formation of six-membered rings by this procedure, and prompt us to report an unsuccessful approach to the cadalene sesquiterpenes which failed due to a preference for the 1,2- rather than 1,4-addition regiochemistry. Further results for non-conjugated aldehydes (ref. 3 and present study) provide a mechanistic rationale for the regiospecificities observed.

A simple artificial light harvesting dyad as a mimic of nonphotochemical quenching in green plants

A carotenoid can efficiently quench the Q y energy of phthalocyanine molecule. Target analysis provides evidence for the pivotal role of the carotenoid excited state in the quenching by showing that the spectrum of the quenching species resembles the carotenoid S 1 spectrum. However, energy transfer involving the carotenoid S 1 state alone cannot be solely responsible for the quenching because the process is solvent polarity dependent. This chapter performs a transient absorption measurement on a model carotenoid with 10 double bonds to gain further insights into the process. Solvent polarity-dependent shape changes that cannot be ascribed to the Sl state are detected. Similar changes are reported for several substituted carotenoids and assigned to an intramolecular charge transfer state. Results show that carotenoids can quench tetrapyrrole singlet excited states by means of energy transfer to optically forbidden carotenoid states. Expanding the conjugated system of the carotenoid by one double bond turns the carotenoid from a nonquencher into a strong quencher.