3-De-oxy-1,2-di-O-isopropyl-idene-5-O-tosyl-d-threo-pentofuran-ose.

In the crystal structure of the title compound, C(15)H(20)O(6)S, the two independent mol-ecules crystalllize in a chiral setting with two different conformations, twisted (4)T(3) and envelope (4)E, for the furan-ose rings. Weak C-H⋯O contacts strengthen the crystal structure.

Dimethyl hydrazine-1,2-dicarboxyl-ate-triphenyl-phosphine oxide (1/1).

In the crystal structure of the title compound, C(4)H(8)N(2)O(4)·C(18)H(15)OP, two triphenyl-phosphine oxide mol-ecules and two dimethyl hydrazine-1,2-dicarboxyl-ate mol-ecules are connected via N-H⋯O hydrogen bonds of moderate strength and are related via a twofold rotational axis. Weak C(ar)-H⋯ O contacts strengthen the crystal structure.

2,6-Anhydro-1,3-di-O-benzyl-d-mannitol.

In the title compound, C(20)H(24)O(5), the six-membered pyran-ose ring adopts a chair conformation. The dihedral angle between the planes of the phenyl groups of the benzyl substituents is 63.1°. Two types of inter-molecular O-H⋯O hydrogen bonds lead to the formation of infinite chains along the b axis. Only weak C-H⋯O contacts exist between neighboring chains.

3'-O-Acetyl-2'-de-oxy-uridine.

In the two independent but very similar mol-ecules of the title compound, C(11)H(14)N(2)O(6), both nucleobase fragments are nearly planar (both within 0.01 Å) while the furan-ose rings exhibit (2)E-endo envelope conformations. In the crystal, the two 3'-O-acetyl-2'-de-oxy-uridine mol-ecules form a pseudosymmetric dimer of two bases connected via two nearly identical resonance-assisted N-H⋯O hydrogen bonds. The resulting pair is further connected with neighboring pairs via two similar O-H⋯O bonds involving the only hydroxyl group of the 2'-de-oxy-furan-ose fragment and the remaining carbonyl oxygen of the nucleobase. These inter-actions result in the formation of an infinite 'double band' along the b axis that can be considered as a self-assembled analogue of a polynucleotide mol-ecule with non-canonical Watson-Crick base pairs. The infinite chains of 3'-O-acetyl-2'-de-oxy-uridine pairs are additionally held together by C-H⋯O inter-actions involving C atoms of the uracyl base and O atoms of carbonyl groups. Only weak C-H⋯O contacts exist between neighboring chains.

6-[Bis(ethoxycarbonyl)methyl]-6-deoxy-1,2;3,4-di-O-isopropyl-idene-d-galacto-pyran-ose.

The title compound, C(19)H(30)O(9), was prepared by substitution at the C6 position in 1,2;3,4-di-O-isopropyl-idene-6-O-trifluoro-methane-sulfonyl-d-galactose using sodium eth-oxy-malonate in dimethyl-formamide. The conformation is skew-boat (0)S(2), slightly distorted towards boat B(2,5). The inflexible pyran-ose structure makes the title compound a suitable inter-mediate for further synthetic work by keeping stereogenic carbon atoms safe from inversion. Several short intra-molecular C-H⋯ O contacts may stabilize the conformation of the mol-ecule. Inter-molecular C-H⋯O inter-actions also occur.

1,2-O-Iso-propyl-idene-ß-d-lyxo-furan-ose.

In the title compound C8H14O5, the pento-furan-ose five-membered ring has a twisted conformation on two carbon atoms while the five-membered ring of the iso-propyl-idene group has an envelope conformation on an oxygen atom. Hy-droxy groups are involved an infinite network of O-H⋯O hydrogen bonds that leads to the formation of a layer parallel to the (001) plane. Only weak C-H⋯O contacts exist between neighboring layers.

1,3-Bis(2-oxoprop-yl)thymine.

In the title compound [systematic name: 5-methyl-1,3-bis-(2-oxoprop-yl)pyrimidine-2,4(1H,3H)-dione], C11H14N2O4, the two 2-oxopropyl groups are nearly perpendicular to the planar thymine unit. One methyl group of oxopropyl substituent is disordered. In the crystal, C-H⋯O inter-actions help to connect the mol-ecules into (001) layers.

Crystal structure of (S)-1-O-tert-butyl-diphenyl-silylglycerol: eight chiral mol-ecules in a triclinic cell.

The asymmetric unit of the title compound {systematic name: 3-[(tert-butyl-diphenyl-sil-yl)-oxy]propane-1,2-diol, C19H26O3Si}, contains eight chiral mol-ecules (Z' = 8). These mol-ecules are connected via a complex system of hydrogen bonds into an infinite assembly along the [100] axis; hydro-phobic tert-butyl and phenyl groups form an external coating of the assembly. These assemblies are packed by weak inter-molecular inter-actions in a peculiar formation resembling a 'header bond' masonry brick wall. Disorder of flexible fragments increases with temperature but the same crystal structure exists from 120 to 220 K (and most probably to the melting point at 334 K).

Amide-Linked Ribonucleoside Dimers Derived from 5'-Amino-5'-deoxy- and 3'-(Carboxymethyl)-3'-deoxynucleoside Precursors(1).

Treatment of tert-butyldimethylsilyl (TBDMS) derivatives of 3'-keto(adenosine or uridine) with [(ethoxycarbonyl)methylene]triphenylphosphorane gave exocyclic alkenes that underwent stereoselective hydrogenation to give 3'-deoxy-3'-[(ethoxycarbonyl)methyl](Ado or Urd) analogues. Saponification provided the 3'-(carboxymethyl)-3'-deoxy(Ado and Urd) derivatives 37 and 38. Treatment of 37 or 38 with DCC and 5'-amino-2',3'-bis-O-TBDMS-5'-deoxynucleosides gave the amide-linked dimers (74-82%). Activation of 37 or 38 with 4-nitrophenol/DCC, and direct coupling of the 4-nitrophenyl esters with 5'-amino-5'-deoxy(Ado or Urd) in pyridine also produced amide dimers efficiently (65-70%). Analogous activation of a 5'-O-DMT-protected carboxylate, and its coupling with 5'-amino-5'-deoxy-2'-O-methyladenosine gave the amide dimer in good yield (74%). Coupling (DCC) of a 5'-azido-2'-O-TBDMS-3'-(carboxymethyl)-3',5'-dideoxyuridine intermediate with 5'-amino-5'-deoxynucleosides gave amide-linked dimers (72-78%) that can serve as masked (azide reduction) 5'-amino dimers for analogous synthesis of extended amide-linked oligomers.

Deoxygenation at the C3 position of D- and L-arabinofuranose: stereospecific access to enantiomeric cordycepose derivatives.

Efficient synthesis of 3-deoxy-1,2-O-isopropylidene-ß-D- and ß-L-threo-pentofuranose (1,2-O-isopropylidene-ß-D- and ß-L-cordycepose) was accomplished starting from D- and L-arabinofuranose derivatives, respectively, by the action of LiBH(Et)3 on corresponding intermediate 3-O-lyxofuranosyl trifluoromethanesulfonates.

D-Arabinose-based synthesis of homo-C-d4T and homo-C-thymidine.

2,3,5-Tri-O-benzyl-D-arabinofuranosyl halides (chloride, bromide) were reacted with AllMgBr, MeMgBr, and VinMgBr to furnish anomeric mixtures of the C-glycosyl products. The factors that influenced the beta/alpha ratio are discussed. The alpha,beta-C-vinyl derivative was transformed into 1-deoxy-1-C-hydroxymethyl-beta- and -alpha-D-arabinofuranoses (2,5-anhydro-D-glucitol and -mannitol, respectively), separable after isopropylidenation step. 2,5-Anhydro-1,3-O-isopropylidene-D-glucitol was converted into 2,5-anhydro-6-O-triphenylmethyl-D-erythro-hex-3,4-enitol and 2,5-anhydro-4,6-di-O-benzoyl-3-deoxy-D-ribo-hexitol, which were coupled with N-3-benzoylthymine under the Mitsunobu conditions to furnish two analogs of nucleosides with a -CH(2)- insert between sugar moieties and thymine.

Protecting groups transfer: unusual method of removal of tr and tbdms groups by transetherification.

The triphenylmethyl (Tr) group undergoes a transfer (transetherification or disproportionation) between the molecules of 5'-O-Tr-2'-deoxynucleosides in a process mediated by anhydrous sulfates of Cu(+2), Fe(+2), or Ni(+2) to yield mixtures of 3',5'-bis-O-Tr and 3'-O-Tr products. If phenylmethanol is present in a reaction medium, detritylation results with concomitant formation of phenylmethyl triphenylmethyl ether. The behavior of t-butyldimethylsilyl (TBDMS) group in 5'-O-TBDMS-2'-deoxynucleosides is exactly the same. Such type of transetherifications was not observed before for the O-Tr and O-TBDMS groups.