Hanson, nomenclature

For the three internal trans-olefins used, because of the Hanson nomenclature, prochiral faces with different names are attacked (Table VI). However, as shown in Scheme 7, the difference in this case is purely formal. In fact, by orienting equally the olefin in the plane of the sheet, with the bulkiest substituent on the left side up, the face of the olefin attacked is in all three cases the same and corresponds to the face attacked in the vinyl olefins. 

For vinyl olefins the face prevailingly attacked by carbon monoxide and hydrogen is always the same and, as shown in Table VI, has the same name according to the Hanson s nomenclature (35). For vinylidene olefins, faces having different names according to Hanson are preferentially attacked (Table VI). As shown in the Scheme 6, if we equally... 

Just as it is convenient to distinguish enantiomers and diastereomers by nomenclature symbols (R, S, E, Z, etc.) it is desirable to provide names for stereoheterotopic ligands or faces. The basic nomenclature to this end has been provided by Hanson 4,6) and is closely related to the nomenclature of stereoisomers. 

In this review, we shall concentrate on the stereochemistry of enzymic reactions of amino acids, many of which involve transformations at prochiral centers. We shall use the nomenclature of Hanson (8) to specify the stereochemistry of prochiral atoms and groups as pro-R (Hjj) and pro-S (Hj) and of prochiral faces as Re and Si and the nomenclature of Mislow and Raban (2) to describe prochiral groups as having enantiotopic or diastereotopic relationships. Reviews on the stereochemistry of enzymic reactions of amino acids were published in 1978 (9,10), and since the seminal review by Dunathan in 1971 (11), several reviews comparing the stereochemistry of pyridoxal phosphate-catalyzed enzymic reactions have appeared (12-15). 

Hanson i described rules that accommodate most situations observed with prochiral centers. The reader is referred to this work for specific examples that do not yield to a simple analysis. The intent of this section is to familiarize the reader with nomenclature and the uses of pro-R and pro-S sites in reactions. 

Helmchen G (1996) A. General aspects. 1. Nomenclature and vocabulary of organic stereochemistry. In Helmchen G, Hoffinann RW, Mulzer J, Schaumann E (eds) Stereoselective Synthesis. Methods of Organic Chemistry (Houben-Weyl), Workbench Edition E21, vol 1,4th edn. Georg Thieme, Stuttgart, New York, pp 1-74 Hirschmann H (1983) Trans N Y Acad Sci Ser II 41 61-69 Hirschmann H, Hanson KR (1971a) Eur J Biochem 22 301-309 Hirschmann H, Hanson KR (1971b) J Org Chem 36 3293-3306... 

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