THE SYNTHESIS AND X-RAY STRUCTURAL STUDIES OF 2-CHOLESTERYL-2-THIO-1,3,2-OXATHIAPHOSPHOLANE AND 2-CHOLESTERYL-2-THIO-1,3,2-DITHIAPHOSPHOLANE

Two ''thiophospholane'' derivatives of cholesterol: 2-cholesteryl-2-th io-1,3,2-oxathiaphospholane (1) and 2-cholesteryl-2-thio-1,3,2-dithiap hospholane (2) were synthesized as new reagents for introducing a chol esteryl moiety at the 5'-end of oligonucleotides via the phosphorothio ate or phosphorodithioate bond. Compounds 1 and 2 were subjected to st ructural studies by X-ray methods. Both compounds crystallized in the orthorhombic system, space group P2(1)2(1)2(1), 1 with a = 6.283(1) An gstrom, b = 12.067(1) Angstrom, c = 38.983(3) Angstrom, 2 with a = 6.3 71(1) Angstrom, b = 11.971(1) Angstrom and c = 39.502(3) Angstrom. The five-membered heterocyclic rings of both compounds attain a half-chai r conformation in the solid state. In structures of 1 and 2 a disorder of some atoms is observed. The absolute configuration at the phosphor us atom in 1 of the components of diastereoisomeric mixture has been e stablished.