Giuseppe Celentano

Poly(Ethylene Glycol)-Supported Proline: A Versatile Catalyst for the Enantioselective Aldol and Iminoaldol Reactions

(2S,4R)-4-Hydroxyproline has been anchored to the monomethyl ether of poly(ethylene glycol), MW 5000, by means of a succinate spacer to afford a soluble, polymer-supported catalyst (PEG-Pro) for enantioselective aldol and iminoaldol condensation reactions. This organic catalyst can be considered as a minimalistic version of a type I aldolase enzyme, with the polymer chain replacing the enzymes peptide backbone, and the proline residue acting as the enzymes active site. In the presence of PEG-Pro (0.25–0.35 mol equiv.), acetone reacted with enolizable and non-enolizable aldehydes and imines to afford β-ketols and β-aminoketones in good yield and high enantiomeric excess (ee), comparable to those obtained using non-supported proline derivatives as the catalysts. Extension of the PEG-Pro-promoted condensation to hydroxyacetone as the aldol donor opened an access to synthetically relevant anti-α,β-dihydroxyketones and syn-α-hydroxy-β-aminoketones, that were obtained in moderate to good yields, and good to high diastereo- and enantioselectivity. Exploiting its solubility properties, the PEG-Pro catalyst was easily recovered and recycled to promote all of the above-mentioned reactions, that occurred in slowly diminishing yields but virtually unchanged ees.

Enantioselective aldol condensations catalyzed by poly(ethylene glycol)-supported proline

Keywords: aldol reactions; asymmetric catalysis; catalyst immobilization; chiral bases; soluble polymers

Poly(ethylene glycol)‐Supported Chiral Imidazolidin‐4‐one: An Efficient Organic Catalyst for the Enantioselective Diels–Alder Cycloaddition

A tyrosine-derived imidazolidin-4-one was immobilized on a modified poly(ethylene glycol) and converted in situ into a soluble polymer-supported catalyst for the enantioselective Diels–Alder cycloaddition of acrolein to 1,3-cyclohexadiene (up to 92% ee) and 2,3-dimethyl-1,3-butadiene (73% ee). Catalyst recycling (up to four cycles) was accompanied by some loss of the chemical efficiency and marginal erosion of the enantioselectivity.

Carotenoids in bird plumage—I. The carotenoid pattern in a series of palearctic carduelinae

Abstract The coloured feathers of Carduelis chloris, Carduelis sinica, Carduelis spinoides, Carduelis carduelis (European and Asiatic), Carduelis spinus, Carduelis citrinella, Serinus serinus and Serinus pusillus were extracted with a new procedure which permits the use of mild conditions (a few minutes at room temperature). After the separation of melanins and proteins, the extracts were analysed by liquid chromatography coupled with mass spectrometry and UV-vis spectroscopy. Two main pigments identified as all trans ϵ,ϵ-carotene-3,3′-dione and 3-hydroxy-ϵ,ϵ-carotene-3′-one were present in all species, accompanied by several cis isomers. In the plumage of C. chloris, C. sinica and C. spinoides significant amounts of lutein were also detected. In the head plumage of C. carduelis more oxidized ϵ,ϵ-carotenoids (C 40 H 52 O 3 and C 40 H 52 O 4 ) were present in all individuals examined.

The chemical structure of the pigments in Ara macao plumage.

Parrots (Psittaciformes) harbor unusually bright, non-carotenoid, feather pigments. We successfully extracted and purified a sufficient quantity of pigment from the red plumage of the Scarlet Macaw (Ara macao) for a partial chemical analysis. The extracts were analyzed by HPLC coupled with UV-VIS and mass spectroscopy before and after total hydrogenation. We found at least four pigment components. We propose a linear polyenal structure comparable with the molecules tetradecahexenal, hexadecaheptenal, octadecaoctenal and eicosanonenal.

Separation and identification of carotenoids in bird's plumage by high-performance liquid chromatography-diode-array detection

The coloured feathers of Carduelis spinus (Siskin), C. flammea (Redpoll), Serinus serinus (Serin), Loxia curvirostra (Crossbill), Pinicola enucleator (Grossbeak), Carpodacus roseus (Pallas Rosefinch) and Pyrrhula pyrrhula (Bullfinch) have been extracted with a new procedure using mild conditions (a few minutes at room temperature). After the separation of melanines and proteins, the extracts were analyzed by HPLC-MS and HPLC-UV-Vis. The main components of the pigments were identified in all the species examined; moreover, UV-Vis and MS data were collected also for the minor components. These data suggest that minor components are generally cis isomers accompanying the predominant all-trans isomers.

Carotenoids in bird plumage: the complement of red pigments in the plumage of wild and captive bullfinch (Pyrrhula pyrrhula)

We have studied the carotenoid pigments in the red plumage of male bullfinch (Pyrrhula pyrrhula) immediately following capture and after the completion of the moult in captivity under dietary control. Astaxanthin, adonirubin, and alpha-doradexanthin, as well as papilioeritrinone and canthaxanthin (in lower amounts) are in every case the dominant carotenoids in the plumage pigment of wild individuals. alpha-Doradexanthin is responsible for the reddish-rose colour, which captive individuals adopt after a diet consisting mainly of lutein as disposable carotenoid. The red pigmentation biogenesis of captive bullfinch is compared with those of other red pigmented Carduelinae in which male individuals usually lose the red colour in captivity, namely Carpodacus roseus, Carpodacus rubricilloides, Uragus sibiricus, Carduelis cannabina, Carduelis flammea, Loxia curvirostra and Pinicola enucleator.

Poly(ethylene-glycol)-supported proline: a recyclable aminocatalyst for the enantioselective synthesis of γ-nitroketones by conjugate addition

A poly(ethylene-glycol)-supported proline was used as the catalyst for two enantioselective conjugate addition reactions leading to γ-nitroketones. In both cases the chemical yield and the stereochemical efficiency of the processes greatly depended on the reaction conditions. In the additions of ketones (cyclohexanone, cyclopentanone, and acetone) to 2-nitrostyrene, fair yields (up to 60%) and good diastereoselectivity (up to 95/5 syn/anti ratios) were observed. The enantiomeric excesses (up to 40%) were lower than those obtained with non-supported proline (e.e. up to 57%). In the addition of 2-nitropropane to cyclohexenone the use of the sodium salt of supported proline allowed to almost match the e.e. of the adduct obtained with rubidium prolinate as the catalyst (50% e.e. versus 59% e.e.) in comparable yields. Examples of recovery and recycling of the supported catalysts in both types of processes were also reported.

CAROTENOIDS IN BIRD PLUMAGE : THE PATTERN IN A SERIES OF RED-PIGMENTED CARDUELINAE

We studied the carotenoid pigments in the red plumage of a series of palearctic Carduelinae (Carduelis cannabina, Carduelis flammea, Carduelis hornemanni, Carpodacus roseus, Carpodacus rubricilloides, Carpodacus trifasciatus, Carpodacus vinaceus and Uragus sibiricus). The pigments were extracted under mild conditions and the extract analysed by HPLC coupled with mass and UV-vis spectroscopy. 4-Oxo-carotenoids are responsible for the red colour in these species. 3-Hydroxy-echinenone is, in every case, the dominant carotenoid in the pigment followed by astaxanthin and adonirubin in variable amounts. 4-Oxo-rubixanthin and 4-oxo-gazaniaxanthin are also present in substantial amounts in some individuals of C. hornemanni and C. roseus. In C. roseus and in C. vinaceus, α-doradexanthin was also identified as an important component of the red colour.

Carotenoids in bird plumage: the complement of yellow and red pigments in true woodpeckers (Picinae)

Woodpeckers typically have colorful, multipatterned plumages. To understand the biochemical basis of the species-specificity of coloration in woodpecker, the complement of carotenoids in the red and yellow feathers of 13 species of true woodpeckers (Picinae) was determined. The pigments were extracted under mild conditions. The extracts were analyzed by HPLC coupled with mass and UV-vis spectroscopy. The 4-oxo-carotenoids (particularly astaxanthin and α-doradexanthin) were responsible for the red colors in these species. Picofulvins were the dominant carotenoids in the yellow feathers of some species. Unmodified lutein, zeaxanthin and β-cryptoxanthin were responsible for the yellow and green colors in other species. Tentative molecular structures for the three main picofulvins are proposed based on the results of spectroscopy (UV-vis, MS) and chemical tests.