Volume 74, Issue 8

This short review covers our contribution in the field of the application of group 6 Fischer carbene complexes toward the synthesis of heterocyclic compounds. Alkenyl and alkynyl carbene complexes are suitable partners in [2+2], [3+2], [4+2], and [4+3] cycloaddition reactions. Moreover, chiral alkenyl carbene complexes react in sequential processes involving an initial Michael addition of a ketone lithium enolate to afford lactones with up to five consecutive stereogenic centers. Based on this strategy, we have devised a new method for the enantioselective synthesis of eight-membered carbocycles.

The palladium-catalyzed substitution reactions forming carbon­carbon and carbon­element bonds, as well as nickel-catalyzed addition of E­H and E­E ' bonds across multiple bonds, are considered in their application to the chemistry of heterocyclic compounds.

Tin-lithium exchange on (2-azaallyl)stannanes affords nonstabilized 2-azaallyllithiums (2-azaallyl anions) that undergo [π4s+π2s] cycloadditions with alkenes to afford pyrrolidines. The scope of this method has been expanded to include 2-azapentadienyllithiums and heteroatom-substituted 2-azaallyllithiums. Alternatively, the (2-azaallyl)stannanes may also be used to generate nonstabilized azomethine ylides via N -alkylation/destannylation or N -protonation/destannylation, and these ylides were also found to be useful for the synthesis of pyrrolidines by [π4s+π2s] cycloadditions with alkenes. Applications of both methods to the total synthesis of alkaloids such as (+)-coccinine, lepadiformine stereoisomers, lapidilectine B, and indolizidine 239CD have been accomplished.

Several highly substituted imidazoles have been under investigation at GlaxoSmithKline as potential therapies for the treatment of rheumatoid arthritis and have spawned the need for a general synthetic method for their preparation on a multikilogram scale. We describe herein the optimization of a general method for the preparation of aryl-substituted TosMIC reagents and the ease with which they undergo [3+2] cycloadditions with a host of imines, prepared in situ, to generate densely functionalized imidazoles with various substitution patterns in a completely regioselective manner.

A new synthesis of sumanirole that is being developed to treat Parkinson's disease is described. The basic skeleton is constructed from 8-hydroxyquinoline and elaborated to the key tricylic intermediate 14. Further elaboration affords a 1,2-amino alcohol, which is converted to an aziridine by a new process. Finally, dissolving metal reduction to open the aziridine and protecting group removal affords sumanirole.

Symmetrical C 40 -carotenoids are efficiently produced by double Wittig olefination of the corrresponding C 15 -phosphonium salts with C 10 -dialdehyde. Industrial syntheses of lycopene-, astaxanthin-, and (3R,3'R)-zeaxanthin-C 15 -phosphonium salts are discussed. An efficient route to a monoprotected C 10 -dialdehyde for the synthesis of unsymmetrical C 40 -carotenoids is presented. Primary polyene allyl alcohols can be converted to the corresponding aldehydes by "TEMPO" oxidation. A high-yield synthesis of meso -zeaxanthin as an example for syntheses of unsymmetrical carotenoids is presented.

Naturally occurring colorants have been used in food processing for centuries to give meals an appealing color. In the first half of the 20th century, the newly discovered brilliant azo dyes, amongst other artificial colorants (indol, triphenylmethane, and methine dyes), were used as pigments for food coloration. The toxicity and/or allergenic potential of some of these colorants were discovered much later. One of these pigments with a critical safety profile is the azo dye tartrazine, which exhibits a nicely fresh greenish-yellow color. The use of tartrazine is now banned in several countries and restricted in others due to its unfavorable safety profile. With the aim of extending the color fan of nature-identical food colorants offered by Roche and therefore offering a less critical colorant to the food industry, a project was initiated at Roche. The goal was to find a safer, naturally occurring pigment with a color hue similar to tartrazine. This paper discusses the process of how such a project is addressed in industry, as well as how promising candidates were selected from the wide variety of the naturally occurring carotenoids. The syntheses of some of these carotenoids will also be described.

A review of literature on photoisomerization of bilirubin and photoactive yellow protein suggests possible involvement of the volume-conserving Hula-twist (HT) reaction mechanism in their primary photochemical processes. Additional definitive experiments to verify their involvement are proposed. Information related to photoproducts of bacteriorhodopsin, rhodopsin, and phytochrome are reviewed. For carotenoids, because of participation of the longer lived triplet state in, for example, the photosynthetic apparatus, the involvement of HT is probably less likely. With the aim of extending the color fan of nature-identical food colorants offered by Roche and therefore offering a less critical colorant to the food industry, a project was initiated at Roche. The goal was to find a safer, naturally occurring pigment with a color hue similar to tartrazine. This paper discusses the process of how such a project is addressed in industry, as well as how promising candidates were selected from the wide variety of the naturally occurring carotenoids. The syntheses of some of these carotenoids will also be described.

The enzyme that catalyzes the central cleavage of β-carotene is an iron monooxygenase. The protein was isolated from chicken intestinal mucosa and overexpressed in two different cell lines. Inductively coupled plasma (ICP) emission analysis revealed that the hydrophobic 60.3-kDa enzyme contains one iron/mole protein. The substrate specificity was investigated, and the reaction mechanism elucidated incubating α-carotene in the presence of highly enriched 17 O 2 and H 2 18 O. A supramolecular enzyme model was synthesized, binding carotenoids K a > 106 mol -1 , which mimics the regiospecific enzymatic cleavage of carotenoids.

Although genes that encode most enzymes of the carotenoid pathway in higher plants have been identified, the regulatory mechanisms that govern the synthesis and accumulation of carotenoid pigments are still obscure. Recent findings relevant to two aspects of carotenoid pathway control are reviewed: availability of substrate and pathway branching. Experimental approaches that are likely to enhance our understanding of carotenoid pathway regulation are also described.

The human macula uniquely concentrates extraordinarily high levels of two xanthophyll carotenoids, lutein and zeaxanthin. The function, metabolism, and physiology of these yellow pigments are incompletely understood, but they are likely to prevent age-related damage to the foveal region by virtue of their ability to act as free-radical quenching antioxidants and to absorb phototoxic blue light with high efficiency. A wealth of circumstantial evidence suggests that high macular levels of these two carotenoids may protect against age-related macular degeneration (AMD), but definitive prospective clinical studies still remain to be conducted. It is imperative to gain a greater knowledge of the basic biochemical and physiological mechanisms underlying the specific uptake and metabolism of lutein and zea-xanthin in the macula and to develop improved methods of quantifying macular carotenoid levels noninvasively in order to facilitate the rational design of successful interventions against the leading cause of irreversible blindness in the elderly in the developed world. The development of resonance Raman spectroscopic methods for the objective measurement of macular carotenoid levels in living humans with and without AMD will be reviewed.

Prostate cancer is the most common cancer in U.S. males. Among potentially beneficial natural compounds is lycopene, which is derived largely from tomato-based products. Recent epidemiologic studies have suggested a potential benefit of this carotenoid against risk of prostate cancer, but not all of the studies have been supportive. The largest prospective dietary study, the Health Professionals Follow-Up Study (HPFS), had found that 2-4 servings of tomato sauce per week were associated with about a 35 % risk reduction of total prostate cancer and a 50 % reduction of advanced prostate cancer in follow-up from 1986 to 1992. Tomato sauce was by far the strongest predictor of plasma lycopene levels in this study. In the largest plasma-based study, high lycopene levels were associated with similar risk reductions for total and advanced prostate cancer. Results from other studies, mostly dietary case-control studies, have been mixed. The reasons for these inconsistencies are unclear. Because lycopene may come from a number of sources, and the bioavailability of lycopene may vary profoundly across these sources, dietary questionnaires are likely to vary markedly in their utility to estimate true variation in body lycopene stores across individuals. With further follow-up in the HPFS, we addressed some possibilities for apparently conflicting results. We confirmed our initial findings with the independent 1992­1998 follow-up period. Our results also indicated various factors may contribute to some of the inconsistencies, including insufficient sample size, low intake of lycopene, failure to account for bioavailability, reliance on a single dietary assessment, and heterogeneity of prostate cancer.

The relationship between tomato products and prostate cancer prevention has been the subject of increasingly intense research activity over the past decade. The hypothesis that tomato products contain phytochemicals, perhaps lycopene and others, that modify prostate carcinogenesis warrants investigation. However, scientists, regulatory agencies, marketers of products, and those defining public health policy have differing opinions regarding the strength of the data when applied to criteria for inference and causality. It is useful to briefly review these criteria and discuss the relative strengths and weaknesses of the published data in order to better define future directions for research. Accepted categories of criteria include: consistency, strength of association, biological gradient, temporality, specificity, biological mechanisms and coherence, and experimental evidence. We believe that continued support for research regarding tomato products, lycopene and other phytochemicals, and prostate cancer risk is warranted and may ultimately serve as the basis for more consistent public health recommendations for the consumer. But, what do we say to the public when the data is still inconclusive? The authors support the recommendation that a minimum of five servings of fruit and vegetables should be consumed daily from a variety of sources. We believe that the hypothesized benefits of tomato products for prostate cancer prevention may be achieved with approximately five servings of tomato products per week. The consumption of lycopene supplements is not currently recommended for prostate cancer prevention or therapy. Future research will allow us to provide more definitive guidelines.

Dietary intake of lycopene is associated with reduced risk of prostate cancer (PCa). We conducted a clinical trial in men with prostate cancer to investigate the biological and clinical effects of lycopene supplementation. Twenty-six men with prostate cancer were randomly assigned to receive a lycopene supplement or no supplement for three weeks before radical prostatectomy. Subjects in the intervention group (n = 15) were instructed to take a tomato oleoresin extract soft gel capsule (Lyc-O-Mato®, LycoRed Company, Beer Sheva, Israel) containing 15 mg lycopene, 1.5 mg phytoene, 1.5 mg phytofluene, and 5 mg tocopherol twice daily with meals. Prostatectomy specimens were evaluated for pathologic stage, Gleason score, volume of cancer, and extent of high-grade prostatic intraepithelial neoplasia (HGPIN). Biomarkers of cell proliferation and apoptosis were assessed by Western blot analysis in benign and cancerous tissue samples obtained from the prostatectomy specimens. Oxidative stress was assessed by measuring the peripheral blood lymphocyte DNA oxidation product 5-hydroxymethyl-deoxyuridine (5-OH-mdU). Plasma levels of lycopene, insulin-like growth factor-1 (IGF-1), insulin-like growth factor binding protein-3 (IGFBP-3), and prostate-specific antigen (PSA) were measured at baseline and after three weeks of study period. After the intervention, more men in the intervention group had smaller (<4 cc) tumors, organ-confined disease without involvement of surgical margins or extra-prostatic tissues, and focal involvement of the prostate with HGPIN compared to the control group. Mean plasma PSA levels were lower in the intervention group compared to the control group. This pilot study suggests that a tomato extract containing lycopene and other tomato carotenoids and phytochemicals may have a potential role in the treatment of prostate cancer. Larger clinical trials are necessary to definitively address potential uses of lycopene or tomato extract in the prevention or treatment of prostate cancer.

Recent observational studies and clinical trials that have investigated the relationship between carotenoids (or diets rich in these compounds) and cervical, breast, ovarian, and colorectal cancer have increased knowledge in this area. Although epidemiological studies suggest a protective association, five randomized controlled trials testing the effect of beta-carotene supplementation on regression of cervical dysplasia, a preneoplastic lesion, did not find an effect on rate of regression. In the Women's Healthy Eating and Living (WHEL) Study, the effects of a high-vegetable carotenoid-rich diet on disease-free survival following treatment for breast cancer is being examined in a randomized multicenter diet intervention trial. Few epidemiological studies of dietary factors and risk for ovarian cancer have been conducted, with mixed results. Early case-control and cohort studies of colorectal cancer have generally suggested a protective effect of vegetable consumption, although a recent large cohort study did not confirm this relationship. In two randomized trials, beta-carotene supplementation was not observed to reduce risk of adenoma recurrence. The Polyp Prevention Trial (PPT), which tested the effect of prescribing increased fruit, vegetable, and fiber intake, and reduced dietary fat, revealed no effect of these efforts on adenoma recurrence in the intent to treat analysis. However, serum carotenoid concentrations were associated with decreased risk of recurrence in that study. To move this area of study forward, more research on mechanisms, surrogate biomarkers, and diet­gene interactions is needed.

Does beta-carotene increase, rather than decrease, human lung cancer rates? A large body of observational epidemiologic study has demonstrated that individuals who eat more fruits and vegetables rich in carotenoids and/or who have higher levels of serum beta-carotene have a lower risk of cancer, particularly lung cancer. This inverse relationship has been particularly strong in lung cancer patients with a history of heavy smoking. However, there is contradictory evidence from recent human intervention studies using beta-carotene supplements (20­30 mg per day). An increase in risk of lung cancer among smokers who took beta-carotene supplements was reported in the Alpha Tocopherol, Beta-carotene Cancer Prevention (ATBC) Trial and among smokers and asbestos-exposed workers in the Beta-Carotene and Retinol Efficiency Trial (CARET), but not among male physicians in the United States in the Physicians Health Study (only 11 % of whom were current smokers). Whether there is a true hazard associated with beta-carotene has been evaluated in control studies using the ferret. This animal mimics the human tissue metabolism of beta-carotene, and has been used for studies of tobacco smoking and inhalation toxicology. In the first study, ferrets were given a high-dose beta-carotene supplement equivalent to 30 mg per day in humans, and exposed cigarette smoke or both for six months. A strong proliferative response in lung tissue and squamous metaplasia were observed in all beta-carotene-supplemented animals, and this response was enhanced by exposure to tobacco smoke. When compared to the control group, beta-carotene-supplemented animals (with or without smoke exposure) had statistically significantly lower concentrations of retinoic acid in lung tissue, and they exhibited reductions in RAR-beta gene expression (a tumor suppressor gene). Further, ferrets given a high-dose beta-carotene supplement and exposed to tobacco smoke had fourfold elevated expressions of c-jun and c-fos genes. In a second study, ferrets were given either physiological- or pharmacologic-dose beta-carotene supplementations, which were equivalent to 6 mg vs. 30 mg per day in humans, respectively. The animals were exposed to cigarette smoke for six months. The retinoic acid concentration and RAR beta-gene expression were reduced in the lung tissues, whereas the expression of AP1, cyclin D1, and proliferative cell nuclear antigen were greater in the high-dose, beta-carotene-supplemented animals with or without smoke, as well as the smoke-exposed, low-dose, beta-carotene-supplemented animalsbut not in the low-dose, beta-carotene-supplemented animals alone, as compared with the control group. Squamous metaplasia was only observed in the lung tissues of high-dose, beta-carotene exposed groups with or without smoke (but not the low-dose beta-carotene plus smoke group, the low-dose beta-carotene-supplemented group, or the control group). These data show that in contrast with the pharmacologic dose of beta-carotene, a physiologic dose of beta-carotene in smoke-exposed ferrets has no detrimental effectand, in fact, may afford weak protection against lung damage induced by cigarette smoke. Further studies from our laboratory have revealed an instability of the beta-carotene molecule in the lungs of cigarette smoke-exposed ferrets. Oxidized beta-carotene metabolites may play a role in lung carcinogenesis: by inducing carcinogen-bioactivating enzymes, facilitating the binding of metabolites of benz[a]pyrene to DNA, enhancing retinoic acid metabolism by P450 enzyme induction with subsequent down-regulation of RAR-beta, and acting as pro-oxidants, causing damage to DNA. Ferret studies under highly controlled experimental conditions using high- and low-dose beta-carotene in the presence of alpha tocopherol and ascorbic acid (thereby stabilizing the beta-carotene molecule) showed protective effects against smoke-induced lung squamous metaplasia in ferrets.

There is extensive evidence that high intake of fruits and vegetables is associated with decreased risk of many types of cancers. Thus, it is widely accepted that diet changes are a powerful means to prevent cancer. Although there is a growing interest in the role of the tomato carotenoid lycopene in cancer prevention and treatment, we hypothesize that a single micronutrient cannot replace the power of the concerted action of multiple agents derived from a diet rich in fruits and vegetables. Indeed, we found that lycopene can synergize with other phytonutrients in the inhibition of cancer cell growth. The mechanism underlying the inhibitory effects of lycopene and other carotenoids involves interference in several pathways related to cancer cell proliferation and includes changes in the expression of many proteins participating in these processes, such as connexins, cyclins, cyclin-dependent kinases, and their inhibitors. These changes in protein expression suggest that the initial effect involves modulation of transcription by ligand-activated nuclear receptors or by other transcription factors. It is feasible to suggest that carotenoids and their oxidized derivatives interact with a network of transcription systems that are activated by different ligands at low affinity and specificity and that this activation leads to the synergistic inhibition of cell growth.

The term "dimensionality" has been used by the analytical chemistry community with several meanings. On different occasions, analysts speak about "two-dimensional" analytical methods, for example, 2D nuclear magnetic resonance spectroscopy, 2D thin-layer chromatography, "two-dimensional" or "three-dimensional" analytical information [1], "two-dimensional" or "three-dimensional" images in surface analytical chemistry, and of " m -dimensional" analytical data [2] obtained, for example, as a result of multicomponent analyses. These examples show that the use of the term "dimensionality" is at times contradictory. This confused position does not promote the unequivocal application of the term "dimensionality" in analytical chemistry. The aim of this document is to provide a concept for the use of the term "dimensionality" as it is related to analytical information.