Hydrogen Bond Assisted l to d Conversion of α-Amino Acids.

l to d conversion of unactivated α-amino acids was achieved by solubility-induced diastereomer transformation (SIDT). Ternary complexes of an α-amino acid with 3,5-dichlorosalicylaldehyde and a chiral guanidine (derived from corresponding chiral vicinal diamine) were obtained in good yield as diastereomerically pure imino acid salt complexes and were hydrolysed to obtain enantiopure α-amino acids. A combination of DFT computation, NMR spectroscopy, and crystal structure provide detailed insight into how two types of strong hydrogen bonds assist in rapid epimerization of the complexes that is essential for SIDT.

Catalytic Stereoinversion of L-Alanine to Deuterated D-Alanine.

A combination of an achiral pyridoxal analogue and a chiral base has been developed for catalytic deuteration of L-alanine with inversion of stereochemistry to give deuterated D-alanine under mild conditions (neutral pD and 25 °C) without the use of any protecting groups. This system can also be used for catalytic deuteration of D-alanine with retention of stereochemistry to give deuterated D-alanine. Thus a racemic mixture of alanine can be catalytically deuterated to give an enantiomeric excess of deuterated D-alanine.

Highly stereoselective recognition and deracemization of amino acids by supramolecular self-assembly.

The highly stereoselective supramolecular self-assembly of α-amino acids with a chiral aldehyde derived from binol and a chiral guanidine derived from diphenylethylenediamine (dpen) to form the imino acid salt is reported. This system can be used to cleanly convert D-amino acids into L-amino acids or vice versa at ambient temperature. It can also be used to synthesize α-deuterated D- or L-amino acids.

Stereospecific synthesis of a twinned alanine ester.

Reaction between 1,2-bis(2-hydroxyphenyl)-ethylenediamine (hpen) and methyl pyruvate gives the diaza-Cope rearrangement product with good yield and excellent stereospecificity. The product containing two chiral quaternary carbon centers is characterized by high performance liquid chromatography and X-ray crystallography. DFT computation provides insight into why the diaza-Cope rearrangement takes place readily with methyl pyruvate but not with other ketones like acetone and substituted acetophenones.

Understanding the interplay of weak forces in [3,3]-sigmatropic rearrangement for stereospecific synthesis of diamines.

Chiral diamines are important building blocks for constructing stereoselective catalysts, including transition metal based catalysts and organocatalysts that facilitate oxidation, reduction, hydrolysis, and C-C bond forming reactions. These molecules are also critical components in the synthesis of drugs, including antiviral agents such as Tamiflu and Relenza and anticancer agents such as oxaliplatin and nutlin-3. The diaza-Cope rearrangement reaction provides one of the most versatile methods for rapidly generating a wide variety of chiral diamines stereospecifically and under mild conditions.

Stereoselective recognition of vicinal diamines with a Zn(II) complex.

Zn(II) complex of L (N,N'-bis(2-pyridylmethyl)-N,N'-dimethyl-trans-1,2-diaminocyclohexane) binds chiral vicinal diamines (1,2-diphenylethylenediamine (dpen) and 1,2-diaminocyclohexane (dach)) stereoselectively. Crystallographic studies reveal that the ternary complex has the C2 symmetric cis-alpha topology. 1H NMR shows that the R,R form of the tetradentate zinc complex binds rapidly and reversibly to the R,R form of the diamine over the S,S form with a stereoselectivity of about 5:1.

A new metal-organic open framework consisting of threefold parallel interwoven (6,3) nets.

Threefold parallel interwoven (6,3) nets were assembled from Ni(II) cyclam complex and 1,3,5-tris[2-(4-carboxyphenyl)-1-ethynyl]benzene. The network generates triangular voids of effective size ca. 18.

A concise, modular synthesis of chiral peraza-macrocycles using chiral aziridines.

[reaction: see text] Novel chiral peraza-macrocycles were synthesized from chiral aziridines as a common building block. Efficient syntheses of chiral [26]-N(6), [12]-N(4), [9]-N(3), and [14]-N(4) systems were accomplished.