Hans Gerlach

Enantiodifferentiation in Taste Perception of the phyllodulcins

Abstract Both enantiomers of phyllodulcin 1 have been prepared. Ester 2 was synthesized in a Wittig reaction from O -benzyl isovanillin. The corresponding stilbene carboxylic acid 3 could be cyclized with CF 3 CO 2 H to produce the 3′-benzyl ether 4 of (±)-phyllodulcin. Acylation with (1 R ,4 S )-camphanoyl chloride gave first 5 and after hydrogenolysis of the benzyl ether group in 5 the diastereomeric esters 6 . The diastereomerically pure 8-(1 R ,4 S )-camphanoate (+) −6 of ( R )-phyllodulcin could be isolated by repeated recrystallization. With (1 S ,4 R )-camphanoyl chloride the enantiomeric 8-(1 S ,4 R )-camphanoate (−) −6 of ( S )-phyllodulcin could be prepared via ent- 5 from a mixture of the diastereomeric esters ent- 6 . Ethanolysis of (+) −6 gave ( R )-phyllodulcin [(+) −1 ] with 99% ee. The enantiomeric (S)-(−) −1 with 98% ee could be obtained from (−) −6 . While (+) −1 , the enantiomer occuring in fermented leaves of amacha, has an intense sweet taste, the enantiomer (−) −1 is completely tasteless.

Synthesis of (S)- and (R)-3-hydroxyhexadecanoic acid

Abstract Diol (R)-(+)- 3 is prepared either from the hydroxyketone 2 by reduction with fermenting bakers yeast or by hydrolysis of the dioxolane (R)-(+)- 1 which is available from dimethyl d -malate as starting material. (R)-(+)- 3 could be converted stereoselectively into (R)-(+)- 4 . Reaction of (+)- 4 with dodecylmagnesium bromide yielded the alcohol (S)-(−)- 5 with >99% ee. Its acetylation gave (S)-(+)- 6 and hydrogenolysis gave the primary alcohol (S)-(+)- 7 which could be oxidized selectively to (S)-(+)- 8 with NaIO 4 RuCl 3 . Alkaline hydroysis of (+)- 8 yielded 3-hydroxyhexadecanoic acid (S)-(+)- 9 which could be esterified to give the methyl ester (S)-(+)- 10 with >99% ee. Starting with the dioxolane (S)-(−)- 1 , derived from dimethyl l -malate, the 3-hydroxyhexadecanoic acid (R)-(−)- 9 and its methyl ester (R)-(−)- 10 could be synthesized via the intermediates (S)-(−)- 3 , (S)-(−)- 4 , (R)-(+)- 5 , (R)-(−)- 6 , (R)-(−)- 7 and (R)-(−)- 8 .

Preparation of (-)-(1S,4R)-Camphanoyl Chloride [2-Oxabicyclo[2.2.1]heptane-1-carbonyl Chloride, 4,7,7-Trimethyl-3-oxo, (1S)-]

Abstract A convenient three step procedure for the preparation of (-)-(1S, 4R)-camphanoyl chloride, starting from (+)-camphoric acid (A) via (-)-bromocamphoric anhydride (B) and (-)-camphanic acid (C) is described.

Analysis of the Electronic Circular Dichroism Spectrum of (−)–[9](2,5)Pyridinophane

The results of a combined experimental and theoretical study of the electronic circular dichroism spectrum of (-)-[9] (2,5)Pyridinophane are presented. The features observed in the measured spectrum in the 180-350 nm wavelength region are reproduced by a series of calculations carried out within a density functional time-dependent approach, coupled with a vibronic analysis allowing rationalizing unambiguously the chiral response of the molecule.

Absolute configuration and circular dichroism of methyl substituted tricarbonyl(1,3-butadiene)iron(0) complexes

Abstract The optically active methyl substituted tricarbonyl(1,3-butadiene)iron(0) complexes (2S,3R,4S)-(−)- 1 and (2R,3S,4R)-(+)- 2 have been synthesized by ionic hydrogenation with Et 3 SiH BF 3 from the acetate (−)-5 and from (+)-10 via (−)-9 in stereoselective reactions. The regioselectivity of the transformation leading from (−)-5 to 1 has been checked with deuterium labelled substrates 6, 7, and 8. An X-ray crystal structure of the (1S,4R)-camphanoate (−)-4 allowed the assignment of the absolute configurations of (−)-3, (−)-5 and hence of (−)-1. The stereoselective reduction of (2R,3R,4S)- 10 via 11 to 9 and the subsequent regioselective isomerization allowed the assignment of absolute configuration to (+)-2. The chiroptical properties of (+)-1 and (+)-2 were determined and compared with those of (2S,3R)-(+)-tricarbonyl(isoprene)iron(0) [(+)-12].

Synthesis and resolution of the enantiomeric trans,trans-spiro[5.5]undecane-1,7-diols and determination of their absolute configuration; (S)-(−)-spiro[5.5]undecane-1,7-dione

Abstract Syntheses of spiro[5.5]undecane-1,7-dione ( 1 ) and the three diastereomeric spiro[5.5]undecane-1,7-diols ( 2 , 3 and 4 ) with cis,cis -, cis,trans - and trans,trans -configuration are described. The structure of the lactone side product (±)-5 was elucidated by NMR spectroscopy. Resolution of the trans,trans -diol (±)- 4 was accomplished via the diastereomeric (1 S ,4 R )-camphanoates (−)- 6 and (+)- 7 to give (−)- 4 and (+)- 4 . Oxidation of (−)- 4 by the method of Swern yielded the optically active dione (−)- 1 . An X-ray crystal structure of (−)- 6 allowed assignment of the absolute configuration of (1 R ,6 S ,7 R )-(−)- 4 and hence of ( S )-(−)- 1 . The chiroptical properties of the bis(4-bromobenzoate) (−)- 8 derived from (−)- 4 also prove the (1 R ,6 S ,7 R )-configuration.

Chirality: A Relational Geometric‐Physical Property

The definition of the term chirality by Lord Kelvin in 1893 and 1904 is analyzed by taking crystallography at that time into account. This shows clearly that chirality is a relational geometric-physical property, i.e., two relations between isometric objects are possible: homochiral or heterochiral. In scientific articles the relational term chirality is often mistaken for the two valued measure for the individual (absolute) sense of chirality, an arbitrary attributive term.

Preparation of optically active 3,9-disubstituted spiro[5.5]undecane derivatives and the determination of their absolute configuration

Abstract The enantiomerically pure 3,9-disubstituted spiro[5.5]undecane derivatives 1 to 8 have been prepared by resolution and their absolute configuration determined by chemical correlation with the known ( aS )-(−)-spiro[5.5]undecane-3,9-diol ( 9 ).