Biosynthesis of crotsparine,crotsparinine and sparsiflorine

The biosynthesis of crotsparine, crotsparinine and sparsiflorine in Croton sparsiflorus has been studied using racemic [Ar-³H]-coclaurine, isococlaurine and norcoclaurine. Tyrosine and coclaurine are shown to be precursors of all three alkaloids.     

Biosynthesis of the bisbenzylisoquinoline alkaloid,tetrandrine

The incorporation of (±)-coclaurine, (±)-norcoclaurine, (±)-N-methylcoclaurine and didehydro-N-methyleoclaurinium iodide into tetrandrine in Cocculus laurifolius has been studied and specific utilization of (±)-N-ethylcoclaurine demonstrated. The evidence indicates that tetrandrine is formed in the plants by oxidative dimerization of N-methylcoclaurine. Double labelling experiment with (±)-N- [¹⁴C]-methyl- [1-³H]-coclaurine demonstrated that the hydrogen atom at the asymmetric centre in the 1-benzylisoquinoline precursor is retained in the bioconversion into tetrandrine. Parallel feedings of (+)-(S)- and (?)-(R)-N-methylcoclaurines showed that the stereospecificity is maintained in the biosynthesis of tetrandrine from the 1-benzylisoquinoline precursor.     

Biosynthesis of papaverine

Tracer experiments have shown that in Papaver somniferum papaverine arises from (−)-norreticuline via norlaudanidine and norlaudanosine.     

Precursors of ricinine in the castor bean plant

Isotopic tracer experiments confirmed that glycerol and succinic acid are good precursors of the pyridine ring of ricinine in castor bean plants. Tritium from C-2 was lost from tritiated glycerol while tritium from C-1 was retained. Thus a derivative of dihydroxyacetone is likely to be intermediate. By simultaneous feeding of glycerol-1-(3)-[³H] and succinic acid-2(3)-[¹⁴C], it was hoped to find precursors of ricinine containing both labels, but none could be found. There was no evidence for the appearance of labeled quinolinic acid, which is presumed to be a precursor of ricinine.     

Biosynthesis of ent-kauranes: Evidence for a C-17, C-16 hydrogen 1,2-shift

The incorporation of ent-kaurenoic acid into the derived hydroxy acid and dihydroxy acid by Beyeria calycina has been studied. The biosynthesis of the hydroxy acid involves a hydrogen 1,2-shift from the C-17 position of ent-kaurenoic acid.     

Biosynthesis of gramine in Phalaris arundinacea

The administration of L-tryptophan-[3-¹⁴C] to Phalaris arundinacea L. (Vantage strain) for 9 days resulted in the formation of radioactive gramine (8.2% absolute incorporation). A systematic degradation of the alkaloid indicated that essentially all its activity was located on the methylene group, indicating that its biosynthesis is the same as that occurring in Hordeum species and Lupinus hartwegii.     

Alkaloid biosynthesis in Croton linearis

The ability of Croton linearis to form crotonosine from linearisine has been demonstrated; the extent of this conversion appears to vary according to the sex of the plant.     

Effects of histidine decarboxylase inhibitors on the production of an aberrant alkaloid in Dolichothele sphaerica

Attempts at regulating the production of the aberrant alkaloid 4(5)-[N-isovalerylaminomethyl]imidazole were initiated by pretreating Dolichothele sphaerica plants with Known histidine decarboxylase inhibitors. Larger quantities of the unnatural precursor, 4(5)-aminomethylimidazole, were converted to the corresponding aberrant alkaloid when the cactus plants were pretreated with α-methylhistidine or α-hydrazinohistidine. These compounds appeared to be successful in inhibiting the formation of histamine from histidine, thereby limiting the availability of the natural precursor.     

Biosynthesis of dioscorine : Incorporation of nicotinic acid into the isoquinuclidine moiety

The administration of nicotinic-[2-¹⁴C] acid to Dioscorea hispida plants afforded radioactive dioscorine (1.9% absolute incorporation) and a systematic degradation of the alkaloid indicated that essentially all the activity was located at C-3. Dioscorine derived from nicotinic-[5,6-¹⁴C, ¹³C₂] acid was also labelled. Its proton noise decoupled ¹³C NMR spectrum contained satellites at C-1 and C-7 due to spin-spin coupling of contiguous ¹³C atoms arising from direct incorporation of the labelled nicotinic acid. A biosynthetic scheme representing a novel utilization of nicotinic acid is proposed.     

The role of strictosidine in monoterpenoid indole alkaloid biosynthesis

In contrast to previous reports that vincoside was the sole precursor for indole alkaloids in Vinca rosea, the 3α epimer strictosidine has been incorporated into tetrahydroalstonine, ajmalicine, catharanthine and vindoline; the anomalous 3β to 3α inversion is no longer required.     

Biosynthesis of withanolides in Acnistus breviflorus: biogenetic relationships among the main withanolides

To excised leaves and 15-day-old seedlings of Acnistus breviflorus sodium [1-¹⁴C]acetate, [2-¹⁴C]mevalonolactone and [¹⁴C-methyl]methionine were administered in separate experiments. From the absolute incorporation values of withaferin A (1), jaborosalactone A (2) and jaborosalactone D (3) isolated at different times after administration of the tracers, it was deduced that compound 2 is a precursor of both 1 and 3 and that the withanolides are later biodegraded to unknown products. Inoculation of [¹⁴C]jaborosalactone A confirmed its transformation into 1 and 3.     

Annonelliptine,an alkaloid from Annona elliptica

Annonelliptine has been isolated from Annona elliptica and its structure has been identified as (R)-7-hydroxy-1-(4′-hydroxybenzyl)-5,6-dimethoxy-N-methyl-1,2,3,4-tetrahydroisoquinoline.     

Biosynthesis of alpinigenine by way of tetrahydroprotoberberine and protopine intermediates

In the biosynthesis of the benzazepine alkaloid alpinigenine a N-methylation step followed by hydroxylation α to nitrogen has now been shown more conclusively to be involved in the transformation of a N-heterocyclic ring system. After feeding Papaver bracteatum plants both the precursors (±)-tetrahydropalmatine-[8,13,14-³H] and (±)-tetrahydropalmatine methiodide-[8,13,14-³H;8-⁴C] an identical mode of abstraction of tritium was observed including a complete loss of the isotope from C-14. The next member in the biogenetic chain, muramine-[8-¹⁴C], was incorporated into alpinigenine very efficiently. Furthermore, using structurally different precursors not utilized for normal alkaloid formation, e.g. 2′-hydroxymethyl-laudanosine-[¹⁴CH₂OH], 13-hydroxymuramine-[8-¹⁴C], the specificity of alkaloid metabolism was examined in the whole plant. Tracer dilution technique was applied to confirm the occurrence in the plant of three established intermediates. Chemical syntheses of four of the alkaloids used during these investigations were developed.     

Iso-erysopinophorine,a new quaternary alkaloid from the seeds of Erythrina arborescens

The ethanolic extract of the seeds of Erythrina arborescens yielded a new quaternary alkaloid provisionally named as iso-erysopinophorine besides the other alkaloids reported previously. The new alkaloid was characterised by chemical and spectral studies.     

Sativanine-g,a cyclopeptide alkaloid from Zizyphus sativa

In addition to the already described peptide alkaloids from the bark of Zizyphus sativa, a new compound of this class, sativanine-G, has been isolated and its structure elucidated. This alkaloid contains a 13-membered ring system and belongs to the nummularine-C class.     

Biosynthesis, accumulation and degradation of theobromine in developing Theobroma cacao fruits

We have studied the purine alkaloid content and purine metabolism in Theobroma cacao fruits at differing growth stages: Stage A (young small fruit, fresh weight, ca. 2 g); stage B (medium size fruit, fresh weight, ca. 100 g) and stage C (large size, fresh weight, ca. 500 g). The major purine alkaloid in stage A fruits (mainly pericarp) was theobromine (0.7 micromol g(-1) fresh weight), followed by caffeine (0.09 micromol g(-1) fresh weight). The theobromine content of the pericarp decreased sharply with tissue age, and the caffeine content decreased gradually. A large amount of theobromine (22 micromol g(-1) fresh weight) had accumulated in seeds (mainly cotyledons) of stage C fruits. Theobromine was found also in the seed coat and placenta. Tracer experiments with [8-(14)C]adenine show that the major sites of theobromine synthesis are the young pericarp and cotyledons of T. cacao fruits. Limited amounts of purine alkaloids may be transported from the pericarp to seed tissue, but most purine alkaloids that accumulated in seeds appeared to be synthesised in cotyledons. Degradation of [8-(14)C]theobromine and [8-(14)C]caffeine to CO2 via 3-methylxanthine and ureides (allantoin and allantoic acid) was detected only in the pericarp of stage C fruits.