Lars Skattebøl

Volatile oil constituents of two Thymus species from Ethiopia.

The volatile oils from Thymus schimperi Ronninger and T. serrulatus Hochst. ex Benth. (Lamiaceae) grown in Ethiopia, have been examined by means of GC and GC–MS. The main constituents of the essential oils of T. schimperi from four regions — Bale, Gonder, Shewa, and Wello — were identified as p-cymene (9–23%), γ-terpinene (8–17%), thymol (6–38%) and carvacrol (5–63%). The oil from T. serrulatus was found to contain p-cymene (13%), γ-terpinene (13%) and thymol (49%) as major components. Both species belong to the thymol–carvacrol chemotypes. Copyright

A simple route to 1-bromobicyclo[1.1.0]butanes by intramolecular trapping of 1-bromo-1-lithiocyclopropanes

Abstract Reaction of the dibromides (5) and (10) with methyl lithium in ether leads to products derived by 1,3-dehalogenation, (6) and (11), whereas (15) and (16) undergo 1,1-dehalogenation and rearrangement to allenes, (17) and (18).

Oxidative degradation of eicosapentaenoic acid into polyunsaturated aldehydes

Abstract Eicosapentaenoic acid is converted in good overall yield to an α,β-ethylenic epoxide derivative. The oxidative cleavage of the epoxide ring with periodic acid in ether proceeded in part with acid-catalyzed rearrangement of the vinyl epoxide moiety prior to cleavage. Among the products were 2E- and 2Z, 5Z, 8Z, 11Z-tetradecatetraenal, 4-hydroxy-2E,6Z,9Z,12Z-pentadecatetraenal and (all-Z)-2-methoxy-3,6,9,12-pentadecatetraenal.

Sulfur-substituted and α-methylated fatty acids as peroxisome proliferator-activated receptor activators

FA with varying chain lengths and an α-methyl group and/or a sulfur in the β-position were tested as peroxisome proliferator-activated receptor (PPAR)α,-δ(β), and-γ ligands by transient transfection in COS-1 cells using chimeric receptor expression plasmids, containing cDNAs encoding the ligand-binding domain of PPARα,-δ, and-γ. For PPARα, an increasing activation was found with increasing chain length of the sulfur-substituted FA up to C14-S acetic acid (tetradecylthioacetic acid=TTA). The derivatives were poor, and nonsignificant, activators of PPARδ. For PPARγ, activation increased with increasing chain length up to C16-S acetic acid. A methyl group was introduced in the α-position of palmitic acid, TTA, EPA, DHA, cis9,trans11CLA, and trans10,cis12 CLA. An increased activation of PPARα was obtained for the α-methyl derivatives compared with the unmethylated FA. This increase also resulted in increased expression of the two PPARα target genes acyl-CoA oxidase and liver FA-binding protein for α-methyl TTA, α-methyl EPA, and α-methyl DHA. Decreased or altered metabolism of these derivatives in the cells cannot be excluded. In conclusion, saturated FA with sulfur in the β-position and increasing carbon chain length from C9−S acetic acid to C14−S acetic acid have increasing effects as activators of PPARα and-γ in transfection assays. Furthermore, α-methyl FA derivatives of a saturated natural FA (palmitic acid), a sulfur-substituted FA (TTA), and PUFA (EPA, DHA, c9,t11 CLA, and t10,c12 CLA) are stronger PPARα activators than the unmethylated compounds.

Synthetic efforts towards the protoilludenes. A formal synthesis of Δ7-protoilludene

Abstract An improved route to 5,8,8-trimethylbicyclo[4.3.0]-4-nonen-3-one, a key intermediate for the synthesis of the protoilludane skeleton and in particular Δ7-protoilludene, is reported. Attempts on an alternative synthesis of Δ6-protoilludene based on a phenylsulfonyl allene cycloaddition reaction is also presented.

Syntheses of some polyunsaturated trifluoromethyl ketones as potential phospholipase A2 inhibitors

Starting from (all-Z)-icosa-5,8,11,14,17-pentaenoic acid [(all-Z)-eicosa-5,8,11,14,17-pentaenoic acid, EPA] and (all-Z)-docosa-4,7,10,13,16,19-hexaenoic acid (DHA) several trifluoromethyl ketones, containing sulfur or oxygen atoms at the β-position, have been synthesized as potential inhibitors of cytosolic phospholipase A2. As part of this work EPA and DHA have been oxidatively degraded to (all-Z)-pentadeca-3,6,9,12-tetraenal and (all-Z)-octadeca-3,6,9,12,15-pentaenal, respectively, in 75% overall yields.

Synthesis of (+) lineatin, an aggregation pheromone component oftrypodendrom Lineatum

Abstract An efficient six-step synthesis of racemic lineatin ( 1 ) is described. The key reaction is a thermal intramolecular ene-allen cyclization.

An adamantane rearrangement. A new pathway

Tricyclo(4.2.2.o1,5)decane (7) in the presence of AlBr3 rearranges partly “forwards” to adamantane (1) and partly “backwards” to tetrahydrodicyclopentadiene (2, largely the oxo isomer). Intermediate 14, characterizing the 7→exo-8→14→3→1 forward pathway, is found only in small amounts. The detection of a new intermediate, 12, also shows that a second major rearrangement route from 7 to 1 is being utilized (see dashed lines in Figure 1).

(1S,5R)-(−)-2,4,4-Trimethylbicyclo[3.1.1]hept-2-en-6-one, from the essential oil of the Ethiopian plant Laggera tomentosa

Abstract Enantiomerically pure (1 S ,5 R )-(−)-2,4,4-trimethylbicyclo[3.1.1]hept-2-en-6-one has been found along with chrysanthenone, thymoquinol dimethyl ether and two stereoisomers of dehydrocitral in the essential oil of Laggera tomentosa , which is endemic to Ethiopia. (1 S ,5 R )-(−)-2,4,4-trimethylbicyclo[3.1.1]hept-2-en-6-one has been identified for the first time from a natural source. Chrysanthenone which is the major constituent of the oil (58%), occurs as the (+)- and (−)-enantiomers in a ca 92:8 ratio.

Coexistence of chrysanthenone, filifolone and (Z)-isogeranic acid in hydrodistillates. Artefacts!

Hydrodistilled oil from leaves of the Ethiopian plant Laggera tomentosa has been shown to contain (-)-chrysanthenone (5%), (-)/(+)-filifolone (92:8; 8%) and (Z)-isogeranic acid (8%)-all likely to be artefacts. The main constituent of the oil, (+)-chrysanthenone (53%), is believed to be the precursor undergoing thermal and solvolytic reactions during the hydrodistillation process.