Tom J. Mabry

Carbon-13 NMR studies of flavonoids. III. Naturally occurring flavonoid glycosides and their acylated derivatives

Abstract 13 C NMR spectra for a variety of flavonoid glycosidcs are presented and analysed. Evidence is presented which demonstrates that 13 C NMR spectroscopy is a valuable technique for distinguishing the sites of methylation, glycosylation and acylation in flavonoid glycoiides, and in some cases the nature and sites of specific sugars and acyl groups. Shifts observed in the spectrum on derivization of the 5-OH group are unusual. The ring size and C-1 configuration in glycosidic sugars are also evident from the spectra. Structural assignments are made for several glycoides.

The Ultraviolet Spectra of Flavones and Flavonols

The methanol spectra of flavones and flavonols exhibit two major absorption peaks in the region 240 – 400 nm1. These two peaks are commonly referred to as Band I (usually 300 – 380 nm, Table V-1 records the λmaxvalues for Band I for all flavones and flavonols examined in the present investigation), and Band II (usually 240 – 280 nm). Band I is considered to be associated with absorption due to the B-ring cinnamoyl system, and Band II with absorption involving the A-ring benzoyl system (see III) [1].

Flavonoid Effects Relevant to Cancer

Flavonoids, such as daidzein and genistein, present in dietary plants like soybean, have unique chemical properties with biological activity relevant to cancer. Many flavonoids and polyphenols, including resveratrol in red wine and epigallocatechin gallate in green tea, are known antioxidants. Some of these compounds have estrogenic (and antiestrogenic) activity and are commonly referred to as phytoestrogens. A yeast-based estrogen receptor (ER) reporter assay has been used to measure the ability of flavonoids to bind to ER and activate estrogen responsive genes. Recently, estrogenic compounds were also shown to trigger rapid, nongenomic effects. The molecular mechanisms, however, have not been completely detailed and little information exists regarding their relevance to cancer progression. As a preliminary step toward elucidating rapid phytoestrogen action on breast cancer cells, we investigated the effect of 17-beta estradiol (E2), genistein, daidzein and resveratrol on the activation status of signaling proteins that regulate cell survival and invasion, the cell properties underlying breast cancer progression. The effect of these estrogenic compounds on the activation, via phosphorylation, of Akt/protein kinase B (Akt) and focal adhesion kinase (FAK) were analyzed in ER-positive and -negative human breast cancer cell lines. E2, genistein and daidzein increased whereas resveratrol decreased both Akt and FAK phosphorylation in nonmetastatic ER-positive T47D cells. In metastatic ER-negative MDA-MB-231 cells, all estrogenic compounds tested increased Akt and FAK phosphorylation. The inhibitory action of resveratrol on cell survival and proliferation is ER dependent. Therefore, all estrogenic compounds tested, including resveratrol, may exert supplementary ER-independent nongenomic effects on cell survival and migration in breast cancer cells.

Ultraviolet-Visible and Proton Magnetic Resonance Spectroscopy of Flavonoids

A number of reviews of ultraviolet and visible absorption spectroscopy have appeared in the past (Jurd, 1962; Mabry et al., 1970; Swain, 1965; Mabry, 1969; Harborne, 1963) the most comprehensive being those of Jurd (1962) and Mabry et al., (1970). The article by Jurd summarizes the work in this field up to about 1960 and gives detailed references to the original spectroscopic work carried out with flavonoids. The book by Mabry et al (1970) updates Jurd’s chapter and in addition provides a detailed catalogue of the ultraviolet (UV) spectra of 175 flavonoids together with comprehensive data on reagent induced shifts for each flavonoid. The present article includes some of the more significant aspects of the earlier reviews and in addition brings them up to date.

Methylated flavonols in Larrea cuneifolia

Abstract Nine of eleven methylated flavonols isolated from Larrea cuneifolia Cav. collected in Argentina have been fully characterized. UV, MS and NMR spectral data are presented for the nine substances all of which were identified as methyl ethers of quercetin and kaempferol. Two of the compounds, 7,3′,4′-trimethylquercetin (II) and 3,7,3′-trimethylquercetin (III), are new natural products. The others are 3,7,3′,4′-tetramethylquercetin (I) (retusine), 3,7-dimethylkaempferol (IV), 7,3′-dimethylquercetin (V) (rhamnazin), 3,7-dimethylquercetin (VI) (kumatakenin), 3,3′-dimethylquercetin (VII), 3-methylkaempferol (VIII) and 3′-methylquercetin (IX) (isorhamnetin). Nordihydroguaiaretic acid (XII) was also detected.

Sesquiterpene lactones — insect feeding deterrents in Vernonia

Abstract Larval feeding tests were run to determine the preference of six species of Lepidoptera for two species of Vernonia which produce sesquiterpene lactones and one which has lost the ability to produce these bitter principles. Significant differences between the feeding preferences of the insect species were observed. Further feeding tests were run with a Vernonia leaf powder medium to determine how interspecific chemical differences influenced these preferences. The sesquiterpene lactone, glaucolide-A, was found to reduce larval feeding when incorporated in a Vernonia powder-agar medium. The amount of insect feeding was inversely proportional to the concentration of glaucolide-A in the medium.

Sesquiterpene lactones from Ambrosia confertiflora (Compositae)

Abstract We describe the isolation and chemistry of four eudesmanolides, reynosin (III), santamarine (IV), α-epoxysantamarine (V), and isotelekin (VII) and the germacranolide parthenolide (VI) from Ambrosia confertiflora collected in Mexico. Most of the populations which afforded one or more of the eudesmanolides also contained the previously described germacranolides, tamaulipin-A (I) and -B (II). Reynosin is a new natural product and this is the first report of epoxysantamarine from a natural source. The determination of ther stereochemistry of the epoxide function as α in epoxysantamarine and the experimental details for the structure determination of tamaulipin-B are reported. Other populations of the species from southwest Texas and north-central Mexico yielded the pseudoguaianolide dilactones, psilostachyin (VIII), psilostachyin-B (IX) and -C (X). Confertin (XI) and peruvin (XII) were isolated from a population of A. confertiflora from Fresnillo, Zacatecas, Mexico.

The cycad neurotoxic amino acid, ß-N-methylamino-l-alanine (BMAA), elevates intracellular calcium levels in dissociated rat brain cells

Seeds of the Guam cycad Cycas micronesica K.D. Hill (Cycadaceae), which contain ss-methylamino-L-alanine (BMAA), have been implicated in the etiology of the devastating neurodisease ALS-PDC that is found among the native Chamorros on Guam. The disease also occurs in the native populations on Irian Jaya and the Kii Peninsula of Japan, and in all three areas the cycad seeds are used either dietarily or medically. ALS-PDC is a complex of amyotrophic lateral sclerosis and parkinsonism dementia complex with additional symptoms of Alzheimers. It is well known that Ca(2+) elevations in brain cells can lead to cell death and neurodiseases. Therefore, we evaluated the ability of the cycad toxin BMAA to elevate the intracellular calcium concentration ([Ca(2+)](i)) in dissociated newborn rat brain cells loaded with fura-2 dye. BMAA produced an increase in intracellular calcium levels in a concentration-dependent manner. The increases were dependent not only on extracellular calcium concentrations, but also significantly on the presence of bicarbonate ion. Increasing concentrations of sodium bicarbonate resulted in a potentiation of the BMAA-induced [Ca(2+)](i) elevation. The bicarbonate dependence did not result from the increased sodium concentration or alkalinization of the buffer. Our results support the hypothesis that the neurotoxicity of BMAA is due to an excitotoxic mechanism, involving elevated intracellular calcium levels and bicarbonate. Furthermore, since BMAA alone produced no increase in Ca(2+) levels, these results suggest the involvement of a product of BMAA and CO(2), namely a beta-carbamate, which has a structure similar to other excitatory amino acids (EAA) such as glutamate; thus, the causative agent for ALS-PDC on Guam and elsewhere may be the beta-carbamate of BMAA. These findings support the theory that some forms of other neurodiseases may also involve environmental toxins.

The structure of psilostachyin, a new sesquiterpene dilactone from ambroisia psilostachya☆

Abstract The structure of psilostachyin, a new sesquiterpene dilactone from Ambrosia psilostachya DC., is shown to be XIII. The synthesis of psilosctachyin from coronopilin provided the stereochemical features shown in XIII.

Sesquiterpene lactones and diterpene carboxylic acids in Helianthus niveus subspecies Canescens

Abstract Three new heliangolides (niveusin-A, -B and -C) and three known diterpene carboxylic acids were isolated and characterized from a CHCl 3 , extract of Helianthus niveus . The structures of the three new lactones were deduced by 1 H and 13 C NMR as well as extensive decoupling experiments and derivatizations.