2' or 3' -deoxy and 2', 3' -dideoxy-beta-L-pentofuranonucleo-side compounds, method of preparation and application in therapy, especially as anti- viral agents

Method for the preparation of 2′- or 3′-deoxy-and 2′,3′-dideoxy-β-L-pentofuranocucleoside compounds of formula I:

• 6
• in which
• B represents a purine or pyrimidine base;
• R1 represents OH;
• R2 and R3 represent, independently of each other, H or OH;
• at least one of R2 and R3 represents H;
• characterized in that the following steps are carried out:
• 1) a compound of formula (II) is condensed with the base B in order to obtain the compound of formula (III) according to the scheme
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• in which formulae (II) and (III)
• R′1 and R′2 have the meanings given for R1 and R2 except that when R1 and R2 represent OH, the said OH group is protected by a protecting group such as an acyl, benzoyl, benzyl or silyl group,
• R′3 represents a C1 to C5 alkyl group or a phenyl radical, which are optionally substituted,
• X is a leaving group such as Cl, Br, I or a C1 to C5 acyloxy or alkoxy group,
• B′ is a purine or pyrimidine base B which is optionally appropriately protected, p2 2) the R′3 CO group at the 2′ position is removed by deacetylation so as to obtain an OH group and a
• compound of formula
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• 3) optionally, the OH group at the 2′ position is removed;
• and
• 4) where appropriate, the R′1 and R′2 groups and the B′ base are deprotected so as to obtain the compounds of formula (I).