Pseudorotational angle

Figure 11.3. The pseudorotation cycle showing the relation between the pseudorotation angle P (0-360°) calculated from the five torsional angles of the furanose.

Conformational analysis of silicon analogues of cyclic phosphates, such as (5) and (6), reveal that they have restricted conformations analogous to those observed for 3, 5 -cyclic nucleotides <90CL97>. The pseudorotation angle (P) obtained for compound (5) is 43.4°. This indicates that the twist conformation 4T3 is in good agreement with the mean value (45°) obtained for 3/,5/-cyclic nucleotides. 

A module for unsubstituted 2-deoxy-cryt/iro-jS-pentofuranose permits the calculation from the pseudorotation angle of all the /ch, 2./ci i, and 3/CH couplings around the furanose ring, except that, in some cases, the relative proportions of the two... 

In the case of furanosides, especially nucleosides, Altona and Sundara-lingam s original symbols for the pseudorotational angle P and pucker (or sometimes (p are used P = is defined as the T2 conformation. Figure 2.4 shows the pseudorotational itinerary, with a nucleoside (sugar D-ribose) as an example. Nucleoside chemists refer to conformations with 0 < P < 36° as N ... 

Figure 3. Sugar pseudorotation phase angles in 400 conformations simulated by Monte Carlo. Left panels evolution of pseudorotation during simulation right panels distribution of pseudorotation. Pseudorotation angles of B- and A-forms are shown in thick lines for comparison.

Fig. 1. Perspective drawing of the E e JT intersection arising for linear coupling (Mexican hat). The rotationally symmetric double cone is located in the figure centre. Also indicated in the figure are the Cartesian displacement coordinates Qx and Qy of the JT active mode, the pseudorotational angle < > and the energy gain Ejt occiuring for the optimum distortion po-...

FIGURE 3.2. Cyd in the anti conformation (a) and Guo in the syn conformation (b). Definition of the giycosidic torsion angle 0CN (= cn) purine nucleoside. In (c) (anti) are also shown the pseudorotational angles of the ribose molecule thus is the angle formed between the planes formed between bonds Oii-Cj. and Cg-C3, and so on. The torsion angle for the syn conformation is also shown (d). 

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