The paper presents results of a comprehensive investigation on the pairing properties of homo-DNA oligonucleotides, the preparation of which has been described in Part IIof this series [2]. The investigation was carried out by using established methods described in the literature for the characterization of oligonucleotides in the natural series, such as determination of melting temperatures of oligonucleotide duplexes by temperature-dependent UV spectrosocpy, determination of thermodynamic data of duplex formation from the concentration dependence of melting temperatures, determination of pairing stoichiometry by ratio-dependent UV spectroscopy of binary mixtures of pairing partners, temperature-dependent CD spectroscopy, gel electrophoresis under non-denaturing conditions, and -in selected cases -'H-and "P-NMR spectroscopy.The systematic comparison of the paring properties of homo-DNA oligonucleotides with corresponding DNA nucleotides (up to dodecamers) indicates that homo-DNA is a highly efficient, autonomous, artificial pairing system with a pairing behavior that is in part similar to, but also, in part, strikingly different from, the pairing behavior of DNA. The pairing properties established so far are listed below in a manner that reflects the sequence of subtitles in Chapt.2 of the text; they were determined under the conditions: H20, 0 . 1 5~ NaCI, 0 . 0 1~ Tris-HC1 buffer, pH 7, oligonucleotide concentrations in the ~L M range, 1 : 1 ratio of single strands in the case of non-selfcomplementary sequences.
This paper describes the preparation of the 2',3'-dideoxy-P-~-glucopyranosyl-( = 2',3'-dideoxy-P-~-eryythro-hexopyranosy1)-derived nucleosides of the five bases adenine, cytosine, guanine, thymine, and uracil ( = 'homo-deoxyribonucleosides') as well as the synthesis of oligonucleotides derived from them. The methods used for both nucleoside and oligonucleotide synthesis closely follow the known methods of synthesis in the corresponding series of natural 2'-deoxyribonucleosides and oligonucleotides. The efficient methods of automated DNA synthesis proved to be fully applicable to the synthesis of homo-DNA oligonucleotides, the only change necessary for achieving satisfactory coupling yields being a slight lengthening of the coupling time. Homo-DNA oligonucleotides with chain lengths of up to twelve nucleoside units were assembled on solid support either manually or on a commercial DNA synthesizer in scales of 0.4 pmol to as much as 200 pmol and were purified by either reversedphase or ion-exchange HPLC to single-peak purity according to both chromatographic systems (estimated purity > 95 %). The choice of the specific base sequences to be synthesized was determined primarily by the constitutional problems of base pairing that emerged from experimental observations made in the course of systematic studies of the pairing properties of homo-DNA oligonucleotides. About 100 homo-DNA sequences were prepared for this purpose. Their pairing properties will he described in Part I11 of this series: the present paper is restricted to the characterization of the purity and constitutional integrity of a few selected (single-stranded) oligonucleotides by 'H-, "P-, and I3C-NMR spectroscopy as well as by FAB and time-of-flight mass spectroscopy.The English Footnotes to Schemes 1-9, Fig.
The synthesis of several substrate analogues of the enzyme b,b-carotene 15,15'-monooxygenase is reported. The substrate specificity of enriched enzyme fractions isolated from chicken intestinal mucosa was investigated. Regarding substrate binding/cleavage, these experiments demonstrate that i) any deviation from the rod-like b,b-carotene structure is not tolerated, ii) one natural, unsubstituted b-ionone ring is required, iii) the position and presence of the Me groups attached to the polyene chain is significant. These results suggest a hydrophobic barrel-like substrate binding site in which the proteins amino acid residues through interaction with the Me groups, direct the central CC bond in binding distance to the active sites metal-oxo center, supporting the unique regiospecificity of cleavage to retinal (provitamin A).
Naturally occurring colorants have been used in food processing for centuries to give meals an appealing color. In the first half of the 20 th 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.
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