Chiral adjunct

Finally, two reports have been made in which chiral adjuncts, a chiral amine341 or a chiral dialkyl phosphite,342 have been used in the preparation of optically active Pudovik-type adducts. 

The reagent has one handicap only (+)-pulegone is readily available. Consequently, Oppolzer and coworkers2 have examined a number of chiral alcohols, derived from various monoterpenes, in which the hydroxyl group is similarly shielded. The endo, e/.r-diphenylmethylisoboraeol (2), obtained from ( + )-camphor, and the enantiomer, obtained from ( —)-camphor, are almost as effective as 1 as chiral adjuncts in this Diels-Alder reaction. 

Boronic ester homologation. (R,R)-2,3-Butanediol- and (-(- )-pinanediol have been used as the chiral adjuncts in a diastereoselective homologation of dichloromethaneboronic esters (1) to the (aS)-a-chloroboronic esters (2). Reaction of 1 with an alkyllithium produces a borate complex (a), which rearranges diastereoselectively in the presence of ZnCl, to 2 with introduction of a chiral center adjacent to boron. The reaction permits... 

Diastereospecific reaction of a Grignard reagent. This reagent has been used as the chiral adjunct in place of 4,6,6-trimethyl-l,3-oxathiane (8, 508-509) in a synthesis of atrolactic acid methyl ether (6) in 97 2% enantiomeric excess... 

This method has been used for a general asymmetric synthesis of amines by a similar mono- or dialkylation of propargylamine using the same chiral adjunct... 

From their QSERR they find solute lipophilicity and steric properties as being responsible for analyte retention (k ) while enantioseparation (a) varied mainly with electronic and steric properties. The main difference between the analytes is that the enantioseparation of the esters is correlated with steric parameters that scale linearly with log a while the sulfoxides scale nonlinearly (parabolic), but this may be due to a computational artifact. The 3D-QSERR derived from field analysis revealed that while superpositioning of field maps for both analytes are not exactly the same, a similar balance of physicochemical forces involved in the chiral recognition process are at play for both sets of analyes. This type of atomistic molecular modeling, then, is a powerful adjunct to the type of modeling described earlier in this chapter and will, no doubt, be used more frequently in future studies. 

Finally, most of the published computational studies directed toward chiral chromatography have been carried out by chromatographers rather than by computational chemists. Most of these scientists look at computational chemistry as an adjunct to their experimental work, but understand the information content derived from molecular simulations can provide valuable information not otherwise available. In that sense they are right. However, most chromatographers are not well versed in computational chemistry and make too many serious errors for their results to be of benefit. So, on the one hand there is a need for computational chemistry but on the other hand too many pitfalls exist for the non-expert to step into. The conclusion one draws from this is that chromatographers should work collaboratively with... 

Piracetam 3 [60a] is medicinally used as anticonvulsant and antiepileptic. Levetiracetam 4 is a chiral second-generation analogue of 3 providing a useful alternative for adjunctive therapy to conventionally anticonvulsants, e.g. benzodiazepines. 

Piracetam (16) [236] is medicinally used as an anticonvulsant and antiepileptic. Levetiracetam (17) is a chiral second-generation analog of 16 providing a useful alternative adjunctive therapy to be used alongside conventional anticonvulsants, for example, benzodiazepines. 

A particular position among such chiral liquid crystal polymers is held by the systems based on cellulose derivatives." They can be classified as cellulose ethers, namely hydroxypropyl cellulose, with some adjunctive ester functions localized normally on the ether branches. The idealized substituted cellobiose repeating unit is represented as follows ... 

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