Biosynthesis of limonoids in Citrus seedlings

Radioactive tracer work showed that nomilinoate A-ring lactone was the predominant, if not the only, limonoid biosynthesized and accumulated in seedlings of lemon, Valencia orange, grapefruit and tangerine. Lemon seedlings were excellent tools for biosynthetic preparation of [¹⁴C]nomilin.     

Biosynthesis of limonoids in Citrus

Analyses of citrus leaves and fruits, and radioisotope tracer work showed that the leaves could synthesize limonoids and that the trees could translocate limonoids from leaves to the fruit. These results suggest that limonoids in citrus fruit tissues are synthesized in leaves and translocated to the fruit. No evidence was found to support the presence of limonoid biosynthetic systems in the fruit tissues.     

Fatty acids of triglycerides from Citrus juice sacs

The fatty acid composition of trigylcerides from oranges, grapefruit, lemons and limes, was determined by GLC. Each species possessed its own intrinsic fatty acid pattern which might be used to differentiate it from the other species. The five major acids in all species were palmitic, palmitoleic, oleic, linoleic and linolenic. Collectively these acids comprised greater than 92% of the total acid content. Lemons were distinguished from all other species by their higher 16/16:1 ratios while grapefruit showed the highest total percentage of 16 and 16:1 acids. Lemons and limes contained higher percentages of branched-chain acids than oranges and grapefruit.     

Distribution of limonoids in the rutaceae

Chemical studies on Choisya arizonica, C. mollis, C. ternata, Esenbeckia hartmanii, Hesperethusa crenulata, Eremocitrus glauca, Triphasia trifolia, Coleonema album and Pamburus missionis are described with special reference to the limonoid bitter principles. The distribution of limonoids in the Rutaceae and especarlly the subfamily Aurantioideae is discussed. Two new coumarins, 7-isopentenyloxy-8-isopentenylcoumiain from Choisya arizonica and C. mollis and 2′,3′-dihydroxydihydrosuberosin from Coleonema album have been isolated and their structures determined.     

Biosynthesis of obacunone from nomilin in Citrus limon

Radioactive tracer work showed that [¹⁴C]nomilin was converted to at least four metabolites in Citrus limon. One metabolite was identified as obacunone, showing that obacunone is biosynthesized from nomilin in C. limon.     

Isofraxinellone,a limonoid lactone from the bark of Fagaropsis glabra

Two lactones, both degraded limonoids, have been isolated from the trunk bark of Fagaropsis glabra. Isofraxinellone is a new natural compound and fraxinellone has previously been characterized in plants of the same family. The structure of isofraxinellone was determined by physical and chemical methods.     

Limonin biosynthesis from obacunone via obacunoate in Citrus limon

Radioactive tracer work showed that [¹⁴C]obacunone was converted to at least four metabolites in Citrus limon. Two were identified as obacunoate and limonin. When [¹⁴C]methyl obacunoate was fed, limonin was found to be one of the metabolites. Based on these results and data accumulated thus far, biosynthetic pathways of limonoids in citrus are proposed.     

Hydrocarbons from epicuticular waxes of Citrus peels

The hydrocarbon fraction of the epicuticular wax layer of peel from 5 cultivars of Citrus was monitored at various stages of fruit development. GLC     

Distribution of limonoids in citrus seeds

Absolute concentrations of the major limonoids in the seeds of 18 cultivars representing eight species in the subgenus Citrus have been determined.     

N-methylflindersine from Spathelia sorbifolia

The isolation and taxonomic significance of N-methylflindersine from S. sorbifolia is discussed.     

Limonoids from Nymania capensis

The bark and timber of Nymania capensis contain prieurianin and other complex limonoids, four of which have been identified. The chemical evidence serves to support the taxonomic position of Nymania in the family Meliaceae.     

Detection of limonoate dehydrogenase activity in albedo tissues of Citrus sinensis

19-Deoxylimonoic acid 3-methyl-¹⁴C ester was converted to 17-dehydro-19-deoxylimonoic acid 3-methyl-¹⁴C ester in albedo tissues of navel oranges. This conversion is direct evidence of limonoate dehydrogenase activity in the tissues.     

Metabolism of phaseollin by Colletotrichum lindemuthianum

Two metabolites of the phytoalexin phaseollin (1) produced by cultures of the fungus Colletotrichum lindemuthianum have been assigned structures (3) and (4).     

Metabolism of exogenous adenine by Acer Pseudoplatanus cells

The cells of Acer pseudoplatanus convert erogenous adenine to various metabolites. The balance between synthesis and degradation of adenine nucleotides has been studied for different adenine concentrations and different periods of incubation. The enzymic pathway mediating the synthesis of adenylic nucleotides from erogenous adenine, and those accounting for the degradation of adenine are discussed, and the deamination of AMP as a possible regulatory mechanism governing the size of the pool of adenylic nucleotides is considered.     

Jangomolide,a novel limonoid from flacourtia jangomas

Jangomolide, a novel limonoid has been isolated, together with limonin, from Flacourtia jangomas.     

Coumarins and psoralens in grapefruit peel oil

Four coumarins, four psoralens and two methoxyflavones were isolated and identified from the peel oil of grapefruit. Five of these compounds are reported as constituents of grapefruit oil for the first time, one of which, 5[(3,7-dimethyl-6-epoxy-2-octenyl) oxy]psoralen is a new natural product.     

Structure and stereochemistry of limonoids of Cabralea eichleriana

From Cabralea eichleriana seeds, the following compounds have been isolated: cabraleone, cabraleadiol, fissinolide, 3-deacetylfissinolide, gedunin, 7-deacetoxy-7-oxygedunin, 7-deacetoxy-7-hyd-roxygedunin, methyl angolensate, and three new compounds, 7-deacetoxy-7-hydroxyphotogedunin, cabralin, and isocabralin. Cabralin has also been obtained by photolysis of fissinolide.     

Metabolism of cholesterol by callus culture of Holarrhena antidysenterica

A chemically defined medium was established for the growth of tissue cultures of Holarrhena antidysenterica. Administration of cholesterol-[4-¹⁴C] to 10-day-old callus yielded radioactive 24-methylenecholesterol, 28-isofucosterol, sitosterol, stigmasterol, and conessine, thereby indicating that the conversion of cholesterol into sitosterol is mediated through 24-methylenecholesterol and 28-isofucosterol in this system.     

Metabolism of nicotine in Nicotiana glauca

A mixture of (?)-nicotine-[2′-³H] and (±)-nicotine-[2′-¹⁴C] was administered to Nicotiana glauca plants for 3 days, resulting in the formation of radioactive nornicotine (49·5% incorporation) and myosmine (2·05% incorporation). Negligible activity was detected in anabasine, cotinine, or 3-acetylpyridine, the last two compounds being added as carriers to the harvested plants. The radioactive nornicotine consisted of 48% (?)-nornicotine-[2′-¹⁴C,³H] and 52% (+)-nornicotine-[2′-¹⁴C]. Thus if (+)-nornicotine is formed from (?)-nicotine the transformation must involve loss of the hydrogen from C-2′. Myosmine is presumably formed from nicotine via nornicotine. However by feeding myosmine-[2′-¹⁴C] to N. glauca it was shown that the dehydrogenation is not reversible, no activity being detected in nornicotine. Nicotinic acid (0·14% incorporation) was a metabolite of myosmine-[2′-¹⁴C]. Essentially all the activity of the nicotinic acid was located on its carboxyl group, indicating that myosmine was a direct precursor.