wherein

A is a covalently bound substituent having a maximum molecular weight of 1000 and is CR₁R₂R₃, wherein R₁, R₂, and R₃ are independently hydrogen, alkyl, cycloalkyl, aryl, arylalkyl, phosphonate, or acylthioalkyl with or without substituents or heteroatoms; or taken together to form a cycloalkyl or aryl ring, with or without substituents or heteroatoms;

X₁, X₂, and X₃ are independently oxygen, methylene, monochloromethylene, dichloromethylene, monofluoromethylene, difluoromethylene, or imido;

T₁, T₂, W, and V are independently oxygen or sulfur;

m=0, 1 or 2;

n=0 or 1;

p=0, 1, or 2;

where the sum of m+n+p is from 0 to 5;

M=H or a pharmaceutically-acceptable inorganic or organic counter ion;

D=O or CH₂;

B is a purine or a pyrimidine residue according to general Formulae IV and V which is linked to the 1′ position of the furanose or carbocycle via the 9- or 1-position of the base, respectively;

Y=H, OH, or OR₄;

Z=H, OH, or OR₅; with the proviso that Y and Z are not both H;

R₄ and R₅ are residues which are linked directly to the 2′ and /or 3′ oxygens of the furanose or carbocycle via a carbon atom according to Formula II, or linked directly to the two 2′ and 3′ oxygens of the furanose or carbocycle via a common carbon atom according to Formula III;

wherein:

O is the corresponding 2′ and/or 3′ oxygen of the furanose or carbocycle;

C is the carbon atom;

R₆, R₇, and R₈ are H, an alkyl, cycloalkyl, aralkyl, aryl, substituted aralkyl, or substituted aryl, such that the moiety defined according to Formula II is an ether; or

R₆ and R₇ are H, an alkyl, cycloalkyl, aralkyl, aryl, substituted aralkyl, or substituted aryl, and R₈ is alkoxy, cycloalkoxy, aralkyloxy, aryloxy, substituted aralkyloxy, or substituted aryloxy such that the moiety defined according to formula II is an acyclic acetal or ketal; or

R₆ and R₇ are taken together as oxygen or sulfur doubly bonded to C, and R₈ is alkyl, cycloalkyl, aralkyl, aryl, substituted aralkyl, or substituted aryl, such that the moiety defined according to Formula II is an ester or thioester; or

R₆ and R₇ are taken together as oxygen or sulfur doubly bonded to C, and R₈ is amino or mono- or disubstituted amino, where the substituents are alkyl, cycloalkyl, aralkyl, aryl, substituted aralkyl, or substituted aryl, such that the moiety according to Formula II is a carbamate or thiocarbanate; or

R₆ and R₇ are taken together as oxygen or sulfur doubly bonded to C, and R₈ is alkoxy, cycloalkoxy, aralkyloxy, aryloxy, substituted aralkyloxy, or substituted aryloxy, such that the moiety according to Formula II is a carbonate or thiocarbonate; or

R₈ is not present and R₆ and R₇ are taken together as oxygen or sulfur doubly bonded to C and both the 2′ and 3′ oxygens of the furanose are directly bound to C to form a cyclical carbonate or thiocarbonate;

wherein:

O is the 2′ and 3′ oxygens of the furanose or carbocycle; and the 2′ and 3′ oxygens of the furanose or carbocycle are linked by a common carbon atom (C) to form a cyclical acetal, cyclical ketal, or cyclical orthoester;

for cyclical acetals and ketals, R₉ and R₁₀ are independently hydrogen, alkyl, cycloalkyl, aralkyl, aryl, substituted aralkyl, substituted aryl, or can be joined together to form a homocyclic or heterocyclic ring composed of 3 to 8 atoms, preferably 3 to 6 atoms; for cyclical orthoesters, R₉ is hydrogen, alkyl, cycloalkyl, aralkyl, aryl, substituted aralkyl, or substituted aryl, R₁₀ is alkyloxy, cycloalkyloxy, aralkyloxy, aryloxy, substituted aralkyloxy, or substituted aryloxy;

wherein:

R₁₁ and R₁₅ are hydroxy, oxo, amino, mercapto, alkylthio, alkyloxy, aryloxy, alkylamino, cycloalkylamino, aralkylamino, arylamino, diaralkylamino, diarylamino, or dialkylamino, where the alkyl groups are optionally linked to form a heterocycle; or

R₁₁ and R₁₅ are acylamino; or

when R₁₁ in a purine or R₁₅ in a pyrimidine has as its first atom nitrogen, R₁₁ and R₁₂ or R₁₅ and R₁₆ are taken together to form a 5-membered fused imidazole ring, optionally substituted on the imidazole ring with alkyl, cycloalkyl, aralkyl, or aryl moieties;

when R₁₅ in a pyrimidine has as its first atom oxygen, R₁₅ and R₁₇ are taken together to form a 5-membered dihydrofuran ring, optionally substituted on the dihydrofuran ring with alkyl, cycloalkyl, aralkyl, or aryl moieties, as described for R₆-R₁₀ above;

J is carbon or nitrogen, with the provision that when J is nitrogen, R₁₃ is not present;

R₁₂ is hydrogen, O or is absent;

R₁₆ is hydrogen, or acyl;

R₁₃ is hydrogen, alkyl, bromo, azido, alkylamino, arylamino or aralkylamino, alkoxy, aryloxy or aralkyloxy, alkylthio, arythio or aralkylthio, or ω-E(C_1-6alkyl)G-, wherein E and G are independently amino, mercapto, hydroxy or carboxyl;

R₁₄ is hydrogen, chlorine, amino, monosubstituted amino, disubstituted amino, alkylthio, arylthio, or aralkylthio, where the substituent on sulfur contains up to a maximum of 20 carbon atoms, with or without unsaturation; and

R₁₇ is hydrogen, alkyl, halo, alkenyl, substituted alkenyl, alkynyl, or substituted alkynyl.