Absolute Configurations ofN,N-Dialkyl α-Amino Acids and β-Amino Alcohols from Exciton-Coupled Circular Dichroism Spectra of Cu(II) Complexes

Abstract

[formula: see text] A circular dichroism technique has been applied to the absolute configurational assignment of acyclic alpha-amino acids and beta-amino alcohols with single stereogenic centers via a one-step derivitization procedure requiring microgram quantities of material. Metal ions fix the geometrical relationship of two chromophores, affording CD spectra that agree with theory on the basis of the expected conformation of the ligands in the metal complexes.

Synthesis and circular dichroism studies of N,N‐bis(2‐quinolylmethyl)amino acid Cu(II) complexes: Determination of absolute configuration and enantiomeric excess by the exciton coupling method

“…1) controls the direction of the propeller twist, we anticipated that derivatization of amino acids and amino alcohols (C and D) would form similar complexes and that ECCD spectra could be correlated to the twist and absolute configuration of the chiral substrate. In our earlier communication, 6 we reported that in situ derivatization of amino acids and amino alcohols followed by addition of Cu(ClO 4 ) 2 and NH 4 SCN uniformly produced ECCD spectra consistent with the known chirality of the complexes (Fig. 2).…”

“…of this material dissolved in THF was added 1.1 eq. of 0.5 N aqueous potassium hydroxide (1,3,4,5,6), or lithium hydroxide (2, 7). The mixture was stirred at room temperature for 40À50 min for 1±6 and 2 days at 80À90°C for 7.…”

“…6 The CD spectra were assigned as a result from an ECCD mechanism, as the inflection points of the CD spectra coincided with the UV maxima of the pÀp * transition of the quinoline arms. It was found that addition of NH 4 SCN increased the amplitudes of the spectra.…”

“…We are interested in copper complexes of N,N-bis [2-quinolylmethyl]amino acid derivatives from several perspectives. Apart from our recent communication describing a simple method of forming these complexes for the determination of amino acid absolute configurations, 6 we also recently reported a study of redox-driven helix inversion using a derivative of methionine. 7 Surprisingly, we have found few literature references to similar complexes.…”

Derivatization, complexation, and absolute configurational assignment of chiral primary amines: Application of exciton‐coupled circular dichroism

“…36,37 A distinguishing feature was the attachment of both chromophores to the same nitrogen atom and fixation of the geometry by complexation with a metal ion. The derivatization protocol afforded a consistent correlation between the absolute configuration of the chiral center and the sign of the CD spectra.…”