Stereoisogram approach

Prochirality and Pro-/ S -Stereogenicity. Stereoisogram Approach Free from the Conventional Prochirality and Prostereogenicity ... 

After we clarify that the conventional approach has not been successful in settling the confusion of these terms, we will demonstrate the stereoisogram approach as a new terminology for settling the confusion. 

In the present stereoisogram approach, the / 5-diastereomer (7 = 7) of 7 is conceptually different from the enantiomer (7) of 7, even if they are identical with each other. The / 5-diastereomeric relationship between 7 and 7 (= 7) is recognized to be superposable on the enantiomeric relationship between 7 and 7. This conceptual feature is emphasized by the recognition of the self-holantimeric relationship between 7 and 7 (= 7) or between 7 and 7 (= 7). 

The stereoisogram approach and the conventional approach will be compared with respect to how the assignment of I S -stereodescriptors is rationalized. 

Table 10.2 Single criterion for giving / S-stereodescriptors of the CIP system in the stereoisogram approach...

Let us examine promolecules of Types I, IH, and V to show a systematic rationaU-zatimi provided by the stereoisogram approach (Table 10.2), where the concept of cMrality-faitlrfulness (Fujita 2009d) assures a systematic but subsidiary linkage between chirality and /tS-stereogenicity, which are independent concepts to each other. 

According to the stereoisogram approach. Type V cases (e.g.. Fig. 10.2) are recognized to be named by the CIP system by virtue of f 5-diastereomeric relationships on the same line as Types 1 and 111. For example, a pair of f 5-diastereomers 2 and 3 located at the horizontal S-axis of Fig. 10.8 is characterized by a pair of f 5-stereodescriptors in terms of such a common priority sequence asa>b>p>p (tentatively specified for the sake of explanation). 

The comparison between Tables 10.2 and 10.3 indicates that the present stereoisogram approach (Table 10.2) shows consistency, while the conventional approach (Table 10.3) lacks consistency from the present viewpoint. 

It should be noted that the enantiotopic relationship detected in Type V by the stereoisogram approach (in a purely geometric meaning) has been excluded from the territoiy of the pro-R/pro-S system by the transmuted term enantiotopic described in Sect. 10.2.5. As a result, the differentiation between the two... 

The problems of the conventional approach pointed out in Sect. 10.2.2, 10.2.4, and 10.2.5 can be more clearly demonstrated as summarized in Table 10.6 by adopting the categories of the stereoisogram approach (Table 10.5). 

In the stereoisogram approach, prochirality of a geometric meaning is characterized by means of a single criterion based on the term enantiotopic (Table 10.5), where such prochirahty emerges in conversions of achiral promolecules into chiral ones, i.e.. Type IV —> I, Type IV —> II, and Type V —> III. 

The stereoisogram approach (Table 10.5) is capable of detecting a coincident appearance of an enantiotopic case and an / 5-diastereotopic case (Figs. 10.7 and 10.13) as well as a coexistence of an enantiotopic case (e.g.. Figs 10.14a and 10.15) and an f S -diastereotopic case (e.g.. Figs. 10.14a and b) in a promolecule (46). The conventional approach (Table 10.6) is completely helpless to detect such interrelations between prochirahty and pro-/ 5-stereogenicity. 

The conventional chirality as a subconcept of the conventional stereogenicity has suffered transmutation apart from the geometric concept of chirality (cf. Item 1 in Sect. 10.2.6), so that it should be replaced by the l S-stereogenicity which is formulated to be independent of chirality in the stereoisogram approach. 

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