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    Union Catalogue of Agricultural Libraries in the Netherlands

    The WUR Library Catalogue contains bibliographic data on books and periodicals held by the libraries of Wageningen University and Research Centre and some 15 associated libraries. Holding data are added to each record.

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Record number 104682
Title [Sigma]-Adducts of pteridines and 3-deazapteridines, structure and reactivity
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[door] A. Nagel
Author(s) Nagel, A.
Publisher Wageningen : [s.n.]
Publication year 1978
Description 92 p.
Notes Proefschrift Wageningen
Tutors Plas, Dr. H.C. van der
Graduation date 1978-06-23
Dissertation no. 730
Author abstract show abstract
In the introduction of this thesis the reactions of pteridines and pyrido[2,3- b ]-pyrazines with nucleophiles are reviewed. In the following chapters the results of an NMR investigation on the formation of σ-adducts between these azaaromatic ring systems and nitrogen nucleophiles, especially KNH 2 /NH 3 , are described. In order to establish the structures of these - not isolable - σ-adducts, the 1H and 13C NMR spectra of pteridine, pyrido[2,3- b ]pyrazine and a number of derivatives of both these heterocyclic systems, containing one or more OCH 3 , SCH 3 , CH 3 , t-C 4 H 9 , OH, NH 2 , NHNH 2 , F, Cl, Br and C 6 H 5 substituents, were extensively analyzed. All resonance signals in the NMR spectra were unequivocally assigned.

By means of 1H and 13C NMR, pteridines are shown to form in principle two different σ-adducts with NH 3 : at -60°C one molecule of NH 3 adds to C-4, yielding 4-amino-3,4-dihydro-2-R-pteridines (R=H, Cl), or alternatively, at temperatures up to +25°C, the addition of two molecules of NH 3 to C-7 and C-6 takes place, causing the formation of 6,7-diamino-4-R-2-X-5,6,7,8-tetrahydropteridines (R=X=H, R=H, X=Cl, OCH 3 , SCH 3 , C 6 H 5 , R=CH 3 , X=Cl. R=C 6 H 5 , X=Cl,H). This detailed NMR spectral information allowed straightforward interpretation of the 13C NMR spectra of the covalent hydrates 3,4-dihydro-4-hydroxypteridine, 6,7-dihydroxy-5,6,7,8-tetrahydroxypteridine and their cationic species.

Due to the rapid decomposition of pteridine in KNH 2 /NH 3 , no σ-adduct could ever be detected. In sharp contrast, three σ-adducts between KNH 2 and pyrido[2,3- b ]-pyrazines are described i.e. the 3-amino-3,4-dihydropyrido[2,3- b ]pyrazinide ion, the 3-amino-2-t-butyl-3,4-dihydro-6-chloropyrido[2,3- b ]pyrazinide ion and the 2-amino-1,2-dihydro-3-phenylpyrido[2,3- b ]pyrazinide ion.

The results are subsequently presented concerning the investigation of the reaction of KNH 2 /NH 3 with 2-X-4,6,7-triphenylpteridines (X=SCH 3 , Cl, F, H). Two reactions are found to take place : aminolysis at C-2, yielding 2-amino-4,6,7-triphenylpteridine (X=SCH 3 , Cl, F) and ring contraction, giving rise to the formation of 2-X-6,8-diphenylpurines (X=SCH 3 , H). By studying the aminolysis with both 15N labelled pteridines and with K 15NH 2 / 15NH 3 it is proved that the displacement at C-2 in the case of X=SCH 3 , occurs via a ring-opening and ring closing sequence [S N (ANRORC)]mechanism to the extent of 50-85% (depending on [KNH 2 ]); in the case of X=F this amounts to 40% and in the case of X=Cl to 100%.

It is further proved that in the ring contraction of 2-methylthio-4,6,7-triphenylpteridine 85% of C-7 is expelled and 10% of C-6, both processes being preceded by addition of amide ion to C-7 and C-6 respectively.

The possible elimination of C-7 and C-6 is clearly demonstrated by the fact that both 4,6- and 4,7-diphenyl-2-methylthiopteridines undergo ring contraction to the same product i.e. 6,8-diphenyl-2-methylthiopurine. As a consequence in the former isomer only C-7 is eliminated, while in the latter exclusively C-6 is expelled.

In the next chapter the reactions of 6-chloro-2-R 1 , 3-R 2 -pyrido[2,3- b ]pyrazines [R 1 =H, R 2 =C 6 H 5 , t -C 4 H 9 , R= t -C 4 H 9 , R 2 =H, R 1 =R 2 =H, CH 3 , C 6 H 5 , phenanthro(9,10)] with KNH 2 /NH 3 are described.

These compounds undergo ring contraction into 2-R-1H-imidazo[4,5- b ]pyridines (R=H, C 6 H 5 , t -C 4 H 9 ), besides reductive dechlorination. It is found that ring contraction of 2,3-diphenyl-6-X-pyrido[2,3- b ]pyrazines takes place exclusively if X=Cl; in the case of X=F only aminolysis is found, and in the case of X=Br reductive debromination occurs exclusively.

The investigation on the mechanism of the ring contraction of 6-chloropyrido-[2,3- b ]pyrazine into 1H-imidazo[4,5- b ]pyridine is performed by using both is 15N-4 and 13C-2 labelled compounds and K 15NH 2 / 15NH 3 . The results can be explained by the initial formation of a σ-adduct of amide ion at C-2 - unfortunately not detectable by spectroscopic methods - in which σ-adduct, by an intramolecular rearrangement, the chlorine atom and C-2 are expelled simultaneously.

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On paper FORUM ; STACKS ; NN08200,730
FORUM ; STACKS ; NN08202,730
Keyword(s) (cab) azines / purines / pyridazines / pyrimidines / chemical structure / chemical reactions / structure activity relationships
Categories Organic Chemistry
Publication type PhD thesis
Language English
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