Chiral molecules and ions are described by various ways of designating their absolute configuration, which codify either the entity's geometry or its ability to rotate plane-polarized light, a common technique in studying chirality.
32.
Thus, it is a powerful technique as VCD spectra of enantiomers can be simulated using " ab initio " calculations, thereby allowing the identification of absolute configurations of small molecules in solution from VCD spectra.
33.
Apart from direct measurement of the optical rotation of an actual sample, it is only possible to determine whether a given chiral molecule will be levorotatory or dextrorotatory directly from its absolute configuration, via detailed computer modeling.
34.
Starting with the substituent of highest priority in the closest ring and moving along the shortest path to the substituent of highest priority in the other ring, the absolute configuration is assigned P for clockwise and M for counterclockwise.
35.
In 1954 he joined R . S . Cahn and Christopher Ingold in their efforts to build a system for specifying a particular stereoisomers by simple and unambiguous descriptors that could be easily assigned and deciphered : The CIP system ( Cahn-Ingold-Prelog ) was developed for defining absolute configuration using " sequence rules ".
36.
Since then its absolute configuration has been elucidated and callystatin A was discovered to have anti-fungal and anti-tumor activities with extreme potency against the human epidermoid carcinoma KB cells ( IG 50 = 10 pg / ml ) and the mouse lymphocytic leukemia Ll210 cells ( IG 50 = 20 pg / ml ).
37.
The absolute configuration of the biologically active form was later determined as ( + )-( 1R, 4S, 5R, 7R )-3, 3, 7-trimethyl-2, 9-dioxatricyclo [ 3.3 . 1.0 4, 7 ] nonane, whereas other enatinomers process no biological attraction activity.
38.
Aasen�s research areas include determination of the absolute configurations of racemic drugs, isolation, structural determination and syntheses of natural products, " e . g . " carotenoids and pyrrolizidine alkaloids, mass spectrometry of specifically deuterium-labelled wax esters, fatty acids and triglycerides, and identification of flavour constituents from tobacco and other plants.
39.
In analysing the constituents of plant signalling, he developed a number of retrosynthetic techniques, including the "'Meinwald Rearrangement "'where an epoxide is converted to a carbonyl in the presence of a Lewis acid; he has also performed substantial research over forty years in NMR spectroscopy . and in reactions for producing chiral derivatives in order to determine absolute configurations of chiral molecules.
40.
Nitric acid oxidation of ( + )-isoserine ( "'3 "') gives ( )-glyceric acid, establishing that ( + )-isoserine also has the same absolute configuration . ( + )-Isoserine can be converted by a two-stage process of bromination and zinc reduction to give ( )-lactic acid, therefore ( )-lactic acid also has the same absolute configuration.
