ステレオへテロトピックな関係ではなくRS-ジアステレオトピックな関係により決定したpro-R/pro-S-記述子

Abstract

The pro-R/pro-S system has been redefined by using the concept of pro-RS-stereogenicity, where two ligands in an RS-diastereotopic relationship are pairwise characterized by pro-R- and pro-S-descriptors on the basis of stereoisograms. As for a practical criterion for determining RS-diastereotopic relationships, a symmetry criterion has been developed as a new matter by extending the concept of stereoisograms to testify RS-diastereotopic relationships. The conventional definitions of pro-R/pro-S-descriptors which are based on the original term "prochirality" (along with enantiotopic and diastereotopic relationships) and on the revised term "prostereogenicity" (along with stereoheterotopic relationships) are altogether abandoned. The revised concept of prochirality has a purely geometric meaning, which stems from the term enantiotopic relationship or equivalently enantiospheric equivalence class (S. Fujita, Symmetry and Combinatorial Enumeration in Chemistry, Springer-Verlag, Berlin-Heidelberg (1991)).The two concepts for describing intramolecular environments, i.e., the pro-RS-stereogenicity and the prochirality, are clarified to correspond to the concepts of RS-stereogenicity and chirality, which have been formulated on the basis of stereoisograms in order to bring about a harmonized viewpoint to stereoisomeric and geometric intermolecular features of stereochemistry (S. Fujita, J. Org. Chem., 69, 3158-3165 (2004); J. Comput. Aided Chem., 10, 16-29 (2009)). Chirality-faithfulness of pro-R/pro-S-descriptors specified by RS-diastereotopic relationships is discussed to harmonize pro-RS-stereogenicity with prochirality.