Thiazole nucleoside

Dioxolane analogues of thiazole nucleosides have been prepared starting from the thiazole derivative (439) which in turn is readily available from 2,2-diethoxyacetamide in a one-pot reaction (Scheme 108) <95TL378i>. 

Thiazolylzinc halides have been employed as nucleophiles in Negishi couplings [12-14]. 2-Thiazolylzinc chloride was prepared by deprotonation of thiazole followed by treatment with ZnCl2. Subsequent Negishi coupling of thiazolylzinc chloride with 5-iodo-2 -deoxyuridine 8 elaborated the 5-substituted pyrimidine nucleoside 9 with the assistance of one equivalent of ZnCl2 [14]. 

F.T. Burling, B.M. Goldstein, Computational studies of nonbonded sulfur-oxygen and selenium-oxygen interactions in the thiazole and selenazole nucleosides. J. Am. Chem. Soc. 114, 2313-2320 (1992)... 

Yadav and Kapoor [13] synthesized the acyclic C-nucleosides (xii) incorporating the thiazole-s-triazine structure as a nucleobase following a three-component, one-pot reaction under solvent free condition and microwave irradiation. 

Yadav and Kapoor [31] investigated the potential of microwaves to accelerate the 3cc reaction between thiazole schifFs base, ammonium acetate and an aldose to diastereoselectively yield the new acyclic C-nucleosides incorporating the thiazolo-5-triazine (xix) structure as the nucleobase. 

Ribavirin, USP. Ribavirin is l-j3-o-ribofuranosyl-l.2.4-thiazole-3-carboxamide. The compound is a purine nucleoside analogue with a modified base and a D-riho.se sugar moiety. The. structure of ribavirin is show n below. 

Cylocondensation of tetra-O-acetyl-a/de/jydo-L-arabinose (143) with l-cysteine gave the thiazol-2-yl C-nucleoside 144 (76LA450). Acetylation of the latter gave the 7-(tetra-6>-acetyl-D-flrafo/no-tetritol-l-yl)thiazolo[3,4-cjoxazole 145 (94M189) (Scheme 44). 

Treatment of the thiazol-2-yl acyclo C-nucleoside 144 with an additional molecule of 137 affected oxazole ring closure of the thiazolo[3,4-c]oxazole acyclo C-nucleoside 146 having two alditolyl chains (76LA450) (Scheme 44). 

B. PYRAZOLO[5,l-i]THIAZOLE ACYCLO C-NUCLEOSIDES 1. Pyrazolo[5,l-b]thiazol-3-yl Acyclo C-Nucleosides... 

C. Imidazo[2,1-6]thiazole Acyclo C-Nucleosides 1. Imidazo[2,l-b]thiazol-5-yl Acyclo C-Nucleosides... 

The term C-nucleoside was only coined after isolation and characterization of the first member of this class pseudouridine, in 1975 [97ACH(ip)]. Before that, alditolyl derivatives of some heterocycles (acyclo C-nucleo-sides) were known both as natural products (alditolyl pteridines or biopterins) as well as products of syntheses (e.g., alditolyl derivatives of imidazoles, benzimidazoles, thiazoles, benzothiazoles, 1,2,3-triazoles, quinoxalines, and flavazoles) and were classified as carbohydrate derivatives of heterocyclic compounds. After isolation of pseudouridine, other naturally occurring members were successively isolated, characterized, and synthesized. It is worth mentioning that synthesis preceded isolation in two cases 9-dea-zaadenosine and pyrrolosine. Comparison with the synthetic compounds facilitated structure elucidation in one case (9-deazaadenosine) and structure reassignment in the other (pyrrolosine). 

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