Mabry Benson

Carbon-13 nmr studies on sitosterol biosynthesized from [13C]mevalonates

[2-13C]Mevalonic acid and [5-13C]mevalonic acid were fed to cultured cells of sunflower and the resulting biosynthesized [13C]sitosterols were examined by 13C NMR spectroscopy. The observations confirmed the biochemically predictable positions of 13C labels in sitosterol. Based on the new information a mechanism for the biogenesis of the C-24 alkyl group in phytosterols is given.

Eight 1,4-naphthoquinones from Juglans

Abstract Eight volatile 1,4-naphthoquinones from acetone extracts of unripe black walnut (Juglans nigra) and English walnut (Juglans regia) fruit were identified by gas chromatography-mass spectrometry assisted by 1H NMR. Compounds not previously reported in walnut are 2-methyl-1,4-naphthoquinone, 2,3-dihydro-5-hydroxy-2-methyl-1,4-naphthalenedione (β-hydroplumbagin), 5-hydroxy-2-methyl-1,4-naphthoquinone (plumbagin), 5-hydroxy-3-methyl-1,4-naphthoquinone and 2,3-dimethyl-5-hydroxy-1,4-naphthoquinone. The latter two compounds are here first reported as natural products.

13C NMR SPECTROSCOPY OF PYRROLIZIDINE ALKALOIDS

Abstract The 13 C NMR spectra of nine pyrrolizidine alkaloids of the macrocyclic diester type, seven of the corresponding N -oxides and of the parent base retronecine have been recorded and the signals assigned. The 13 C NMR signals were found to be sensitive to structural variation in both the diester moiety and the heterocyclic ring system, providing useful information for structural elucidation, particularly when the 1 H NMR spectra may be difficult to interpret.

Odor thresholds of various branched esters

A series of branched esters (methyl 2,2-dimethylpropanoate to ethyl 2-ethylhexanoate) were purified by preparative gas chromatography and their odor thresholds were determined using sensory panel methods. The odor thresholds reached a minimum with the butanoate and pentanoate esters. In general, the branched esters have much lower odor thresholds than their straight chain counterparts. Replacing methyl and ethyl branch substituents with mercapto- or hydroxy-groups resulted in higher odor thresholds.

The location of the methylol groups in sapogenol C and erythrodiol and its biosynthetic significance

Abstract The 13C NMR spectra of erythrodiol and sapogenol C have been determined and assignments made for all 30 carbons in each compound. This has permitted a hydroxyl group of sapogenol C to be located at C-24. The biosynthetic significance of sapogenol C and erythrodiol production by oxidation of β-amyrin is discussed.

Metabolism of mevalonic acid to long chain fatty alcohols in an insect

Abstract A mixture of long chain fatty alcohols (LCFA) with chain lengths of 24 to 30 carbon atoms, as free and esterified components, have been isolated from the aphid, Schizaphis graminum . Both radiolabelled mevalonic acid and palmitic acid served as effective precursors in the synthesis of LCFA. This is the first time that the trans -methylglutaconate shunt has been shown to be operational for fatty alcohol synthesis and to occur in a lower-evolved animal.

The characterization and absolute stereochemistry of barbaline, a diterpenoid alkaloid from Delphinium barbeyi

The structure and absolute stereochemistry of a new diterpenoid alkaloid, barbaline, was determined by NMR spectroscopy techniques and single-crystal X-ray diffraction analysis.

Conformational analysis of 10α-cucurbitadienol

Evidence has been obtained on the solid state (determined by X-ray crystallography) and solution (determined by 1H and 13C NMR spectroscopy) properties of 10α-cucurbita-5,24-dien-3β-ol which indicate that the molecule orients into a bent rather than flat conformation, the 3β-OH group aligns into the unusual axial rather than the equatorial position, and the side chain orients into the right-handed conformation.

Minor petuniasterones from Petunia hybrida

Abstract Seven new steroids have been isolated from leaves and stems of Petunia hybrida . They are 30-hydroxy petuniasterone A (C-30 epimeric mixture), 1α-acetoxy-1,2-dihydropetuniasterone A (designated petuniasterone E), (22 R ,24 S )-7α,24-dihydroxy-22,25-oxidoergosta-1,4-dien-3-one (petuniasterone F), C-24 epimers of (22 R )-7α,22,24,25-tetrahydroxyergosta-1,4-dien-3-one (petuniasterones G 1 and G 2 and C-24 epimers of (22 R )-1-α-acetoxy-7α,22,24,25-tetrahydroxyergost-4-en-3-one (petuniasterones H 1 and H 2 ). The compounds which have 1-α-acetoxy groups may easily be converted into the corresponding A-ring dienes by mild base. The orthoesters and other side-chain variants may be formed from the 24,25-epoxy compounds which co-occur in the plant.

Ergostanoids from Petunia parodii

Abstract Leaves of Petunia parodii gave three new petuniolides, one of which has a 9,11-double bond. Of the other two, one has a 9β-OH with an 11,12-double bond and the second has a 9β, 19-cyclopropyl system as well as an 11β-OH and a 12-keto group. Also present are six new petuniasterones which arise from rearrangement of the D-ring epoxides, petuniasterones K and L. A 13,17- seco -petuniasterone was also present.