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Kondensation des D‐Arabinofuranosylthioimidates (I) mit den Hydrazinopyridinen (II) und (IV) bzw. dem Hydrazinopyrazin (VI) gibt die C‐a‐Arabinofuranosylnucleoside (IIIa), (Va), (Vb) bzw. (VIIa), die durch Folgereaktionen in die Derivate (IIIb),(Vc)‐(Vg) bzw. (VIIb)‐(VIIe) übergeführt werden (Strukturuntersuchungen).

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signals at 2.5-2.S, and (2) the absence of an AcO-1 and a H-l signal at 2 and 6, respectively. The remaining absorptions closely resembled those of 3. A careful analysis of the 400-MHz spectrum with the aid of decoupling experiments therefore established the structure 5 for this product. The elementary analysis and mass spectrum supported the structure. The mechanism for the formation of such a further reduced P sugar is, however, currently under investigation.The values of the geminal P-C-H coupling constants (e/1|P) of the presently described phosphinyl coompounds apparently depend upon the magnitude of their approximate 0=P-C-H dihedral angles illustrated in the Newman projections (Figure 1). Thus the anti conformation of the 0=P-C-H group exhibited a lower magnitude of coupling than the gauche conformation, providing a quick method for assignment of configuration of the P sugars. A similar dependence of the geminal P-C-H coupling constant of the 0=P-C-H dihedral angle has been reported for a linear and cyclic phosphonyl compound.5 The large values of the H-C-5-P geminal

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