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Acylation of a 6-(Methylamino)-5-nitrosopyrimidine and 1,3-Dipolar Cycloaddition of an 8-Methylisoxanthopterin N(5)-Oxide. Synthesis of C(6),N(8)-Disubstituted Isoxanthopterins

✍ Scribed by Thomas Steinlin; Andrea Vasella

Publisher
John Wiley and Sons
Year
2009
Tongue
German
Weight
386 KB
Volume
92
Category
Article
ISSN
0018-019X

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✦ Synopsis

Abstract

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Acylation of 2‐amino‐4‐(benzyloxy)‐6‐(methylamino)‐5‐nitrosopyrimidine (5) with acetic anhydride or chloroacetic anhydride in the presence of 4‐(dimethylamino)pyridine (DMAP) led to the C(2)‐acylamino derivatives 6 and 7, respectively. In the absence of a base, acetylation did not lead to a product, while chloroacetylation led to the 6‐chloropteridine 11. Chloroacetylation in the presence of Hünig's base provided the pteridinone N(5)‐oxide 10, suggesting that acylation of 5 is readily reversible, and that the unfavourable equilibrium must be displaced by a follow‐up reaction to trap the acylation product. Acylation of 5 with hexadienoyl chloride, followed by intramolecular Diels–Alder reaction, provided the pteridinone 12. A high yielding 1,3‐dipolar cycloaddition of the acylnitrone 10 to electron‐poor and electron‐rich dipolarophiles, followed by spontaneous N,O‐bond cleavage, gave the C(6)‐substituted pteridinones 19a–19e that were deprotected to the pteridine‐4,7(3__H__,8__H__)‐diones 20a–20e. Substitution of the 6‐chloropterin 11 provided the 6‐morpholinopteridine 25. Sonogashira coupling yielded the fluorescent [(pteridin‐6‐yl)ethynyl]‐glucopyranoside 26, 6‐ethynylpteridine 28, and 6,6′‐(ethynediyl)bispteridine 29. The alkyne 28 reacted with Me~3~SiCl and LiBr in MeCN to produce the bromoalkene 31.

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