Hans Johan Storesund

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

Formation of 2,3-pentanediol from 2,3-pentanedione and acetylethylcarbinol by diacetyl(acetoin)reductase from Aerobacter aerogenes. A possible new pathway.

Diacetyl(acetoin)reductase catalyzes the reversible reduction of acetoin (acetylmethylcarbinol) to 2,3butanediol and the irreversible reduction of diacetyl to acetoin [ 1,2] . The enzyme has been characterized kinetically and found to follow an ordered bi-bi mechanism [3,4] . During work with the three enzymes leading from pyruvate to 2,3-butanediol, fig. 1, we have observed that the first enzyme, the pH 6 acetolactate-forming enzyme, in addition to forming acetolactate from pyruvate, is able to form acetohydroxybutyrate from pyruvate and 2-oxobutyrate [S] . This enzyme requires cocarboxylase and Mn2+ for its activity [6,7] . The second enzyme, acetolactate decarboxylase, decarboxylates acetolactate or acetohydroxybutyrate to yield acetoin or acetylethylcarbinol, respectively [8]. In the present report, we have shown that the substrates for diacetyl(acetoin)reductase, diacetyl, acetoin, and 2,3-butanediol, can be replaced by their respective analogues 2,3-pentanedione, acetylethylcarbinol, and 2,3-pentanediol.

(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.

Constituents of the Essential Oil of Laggera tomentosa Sch. Bip. ex Oliv. et Hiern Endemic to Ethiopia

Abstract The essential oil from Laggera tomentosa Sch. Bip. ex Oliv. et Hiern (Asteraceae) endemic to Ethiopia was investigated by means of GC, GC/MS and NMR spectroscopy. Forty-nine compounds constituting 94% of the oil were identified. The oil composition was characterized by a high percentage of oxygenated monoterpenes (78%), the major compound being chrysanthenone (58%). Sesquiterpene hydrocarbons constituted 10%, while the monoterpene hydrocarbons and oxygenated sesquiterpenes accounted for 3% each. The high percentage of chrysanthenone and the other main compounds isochrysantenone, filifolone and (Z)-isogeranic acid made the composition of the oil markedly different from those of the other species of the genus.

Classical carbonium ions. Part 13. Rearrangements from secondary to primary alkyl groups during reactions involving carbonium ions

The rearrangement of cyclohexylamine to cyclopentylmethyl derivatives, earlier reported in brief, is confirmed. A similar reaction with 4-trans-t-butylcyclohexylamine is shown to give trans-3-t-butylcyclopentylmethyl derivatives, defining the conformational requirements and stereochemical course of the rearrangement. In similar reactions 2-butylamine and 3-pentylamine give, in small yield, derivatives of primary alcohols. Cyclohexyl toluenesulphonate probably gives a very small yield of cyclopentylmethyl acetate. All these reactions involve the formation of products formally derived from carbonium ions much less stable than those initially generated, and yields, though small, are much larger than can be accounted for by classical descriptions. It is proposed that corner-protonated cyclopropanes (‘non-classical carbonium ions’) are ‘intermediates’ of very short lifetime in these reactions; the extent to which it is possible to regard species of very short lifetime as intermediates is discussed.

Nucleophilic substitution reactions of allylic halides carrying electron-withdrawing substituents in the γ-position. Formation of cyclopropanes from dimethyl 2-bromo-2-methylpropylidenemalonate

Reaction of dimethyl 2-bromo-2-methylpropylidenemalonate with sodium methoxide or potassium cyanide in methanol produces cyclopropane derivatives in high yields, thus indicating an overall substitution with nucleophilic attack occurring at the β-position of the allylic halide.

Volatile Oil of Becium grandiflorum subsp. grandiflorum (Lam.) Pic. Serm. from Ethiopia

Abstract The essential oil of Becium grandiflorum subsp. grandiflorum, a perennial aromatic shrub endemic to Ethiopia, was analyzed by GC and GC/MS. The major components of the oil were, in addition to three unknown constituents (10.0%, 9.7%, and 1.7%, respectively) identified as (Z)-β-ocimene (17.6%), myrcene (8.4%), limonene (8.0%), and β-caryophyllene (7.6%).

Evidence for C–C σ-delocalisation in simple secondary carbonium ions; secondary → primary rearrangements

Small yields of primary acetates are obtained in the acetolysis of typical secondary N-alkyl-N-nitrosoacetamides; they imply strongly endothermal rearrangements in the cationic intermediates, best explained by C–C σ-delocalisation or ‘non-classicism.’