How to use Kits

Choosing the kits

Depending on the amount of racemate available, budgetary constraints, as well as the availability of analytical setup, you can decide which and how many kits you should use for screening. There are 4 kits available per racemate. For exhaustive screening and to ensure that you have not missed an optimal resolving agent/solvent combination, we recommend that you use all 4 kits during the experiment. For primary screening kits, 3 mmol per kit is needed during the experiment. If the amount of racemate available is less, and if you have chiral HPLC available for screening, you may prefer to use the kits with glass vials. If the racemate is acidic, you should use the base kits. On the other hand, if the racemate is of type base, you should use acidic kits. For neutral racemates of type alcohols, amino acids, aldehydes and ketones derivativization to acidic or basic state is required before using the kits.

Screening Procedure

The experiment involves the following steps:

Pre-processing of Alcohols

Alcohol is neutral in functionality and it is usually resolved by conversion into the mono-ester of succinic or phthalic acid. This hydrogen succinate or phthalate then gets converted into a diastereomeric salt with optically active bases. Steps:

Pre-processing of Amino Acids (Amphoteric Racemate)

Amino acids exist in Zwitter ionic structure. A synthetic amino acid is primarily resolved using one of two types of methods:


a) Protection of Carboxylic Group using Esterification The carboxyl end of the molecule can be protected by esterification followed by diastereomeric salt formation of free amine function and needs screening kits of type A1, A2, A3, A4. Many racemic alpha-amino acids have been successfully resolved by preparing isobutyl or benzyl esters.
Steps:
  • Add a sufficient amount of dilute HCl to the racemate to dissolve it and bring the pH to 3
  • Cool the mixture to 0 to 2 º C
  • Esterify by adding (1:1.2 ratio) of isobutyl or benzyl ester
  • Heat the mixture to 100 º C and then cool it to 0 to 5 º C
  • Decrease the acidity to ph 7 by adding NaOH.
  • Use the kits A1, A2, A3, A4 as described here to get the diastereomeric salt
  • After having identified the ideal candidate vial, remove the ester group introduced in step 3 under mild hydrolysis conditions and verify that no racemization occurs

  • b) Protection of Amino Group using Formylation The carboxylic group can be screened with the ChiroSolv® kits B1, B2, B3, B4. After having identified the ideal candidate vial, remove the formyl group under mild hydrolysis conditions and verify that no racemization occurs.
    Steps:

    Preprocessing of Aldehydes and Ketones

    In order to be resolved by salt formation, aldehydes and ketones must be converted into either acidic or basic derivatives.


    a) Acidic derivatives Reagents like 4-sulfonylphenylhydrazine, 4-(4-carboxyphenyl) semicarbazide, 4-hydrazinobenzoic acids (para/meta), or Oxalic acids monohydrazide can be used. These salts can then be resolved by chiral bases.
    Steps:
    b) Basic derivatives Carbonyl can be converted into enamine using tertiary amines, which can then be resolved by chiral acids. Alternatively, carbonyl can be treated with bisulphite salts of chiral amines, and the resulting diastereomers can be separated by crystallization
    Steps:

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