Application of optically active aminonaphthols as NMR solvating agents for chiral discrimination of mandelic acid

A series of optically active aminonaphthol derivatives were prepared and screened as chiral solvating agents to discriminate the CαH of racemic mandelic acid by 1H NMR analysis. An effort was made to establish a correlation of the structure of aminonaphthol derivatives and the selectivity in this non-covalent interaction. A linear relationship between the experimental and calculated enantiomeric purity was established by indicating the potential use of the system to determine the ee for the samples of mandelic acid of unknown enantiomeric purity.

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[(2-Methoxynaphthalen-1-yl)phenylmethyl]-methyl(1-phenylethyl)amineC27H27NO[α]D25 = +61.6 (c 0.753, CHCl3)Source of chirality: (S)-(−)-1-PhenylethylamineAbsolute configuration: (S,S)

[(2-Isopropoxynaphthalen-1-yl)phenylmethyl]-(1-phenylethyl)amineC28H29NO[α]D25 = −71.1 (c 1.0, CHCl3)Source of chirality: (S)-(−)-1-PhenylethylamineAbsolute configuration: (S,S)

[(2-Butoxynaphthalen-1-yl)phenylmethyl](1-phenylethyl)amineC29H31NO[α]D25 = −45.6 (c 1.0, CHCl3)Source of chirality: (S)-(−)-1-PhenylethylamineAbsolute configuration: (S,S)

[(2-Benzyloxy-naphthalen-1-yl)-phenyl-methyl]-(1-phenyl-ethyl)-amineC32H29NO[α]D25 = −68.6 (c 1.0, CHCl3)Source of chirality: (S)-(−)-1-PhenylethylamineAbsolute configuration: (S,S)

{[2-(4-Bromobenzyloxy)naphthalen-1-yl]-phenyl-methyl}-(1-phenylethyl)amineC32H28BrNO[α]D25 = +44.2 (c 1.38, CHCl3)Source of chirality: (S)-(−)-1-PhenylethylamineAbsolute configuration: (S,S)

{[2-(3,5-Dibromo-benzyloxy)-naphthalen-1-yl]-phenyl-methyl}-(1-phenyl-ethyl)-amineC32H27Br2NO[α]D25 = +66.1 (c 1.0, CHCl3)Source of chirality: (S)-(−)-1-PhenylethylamineAbsolute configuration: (S,S)

{[2-(4-Fluorobenzyloxy)naphthalen-1-yl]-phenylmethyl}-(1-phenylethyl)amineC32H28FNO[α]D25 = +61.3 (c 1.0, CHCl3)Source of chirality: (S)-(−)-1-PhenylethylamineAbsolute configuration: (S,S)

{[2-(4-Methoxy-benzyloxy)naphthalen-1-yl]-phenylmethyl}(1-phenylethyl)amine (S,S)-15C33H31NO2[α]D25 = +59.0 (c 1.01, CHCl3)Source of chirality: (S)-(−)-1-PhenylethylamineAbsolute configuration: (S,S)

Toluene-4-sulfonic acid 1-[phenyl-(1-phenyl-ethylamino)methyl]naphthalen-2-yl esterC32H29NO3S[α]D25 = +11.15 (c 1.01, CHCl3)Source of chirality: (S)-(−)-1-PhenylethylamineAbsolute configuration: (S,S)

Toluene-4-sulfonic acid 1-{[methyl-(1-phenylethyl)-amino]phenylmethyl}naphthalen-2-yl esterC33H31NO3S[α]D25 = +296.8 (c 0.44, CHCl3)Source of chirality: (S)-(−)-1-PhenylethylamineAbsolute configuration: (S,S)

{1-[Phenyl(1-phenylethylamino)methyl]-naphthalen-2-yloxy}acetic acid ethyl esterC29H29NO3[α]D30 = +185.6 (c 0.7, CHCl3)Source of chirality: (S)-(−)-1-PhenylethylamineAbsolute configuration: (S,S)

2-{[(2-Hydroxynaphthalen-1-yl)phenylmethyl]-amino}-3-methylbutyric acid methyl esterC23H25NO3[α]D25 = +428.0 (c 0.36, CHCl3)Source of chirality: l-Valine methyl ester hydrochloride saltAbsolute configuration: (S,S)