S.K. Roy

Optical rotatory dispersion and absolute configuration—III : Pyrrolidine, piperidine and tetrahydroisoquinoline alkaloids

Abstract Optical rotatory dispersion measurements on pyrrolidine, piperidine, and tetrahydro-isoquinoline alkaloids indicate that the absolute configuration of the α-asymmetric center may be assigned directly from the dispersion curve, provided either that the nitrogen atom is not protonated, or that the compound contains a chromophore absorbing above 200 mμ.

Optical rotatory dispersion and absolute configuration—I : α-Amino acids☆

Abstract Optical rotatory dispersion measurements of six enantiomeric pairs of α-amino acids, both in neutral and in acidic solution, have shown that the direction and slope of the ORD curve between 200 and 225 mμ will indicate the absolute configuration of the α-asymmetric center.

Optical rotatory dispersion and absolute configuration—IV: α-Substituted alcohols and their derivatives

Abstract Optical rotatory dispersion measurements on α-hydroxy acids, α-substituted alcohols, and their derivatives indicate that a knowledge of the dispersion curve between 200 and 225 mμ permits the direct assignment of the absolute configuration of these compounds. In this way the configurational identity of d -glyceric acid, d -serine, d -lactic acid and d -alanine with d -glyceraldehyde has been confirmed, and compounds derived from, or related, to, α-substituted alcohols may thus be correlated with d -glyceraldehyde.

Optical rotatory dispersion and absolute configuration—II : Aporphine alkaloids

Abstract The absolute configuration of aporphine alkaloids may be simply determined from the sign of their high-amplitude Cotton effect centered at 235−245 mμ.

Optical rotatory dispersion and absolute configuration—X α- and β-phenylethylamine S

Abstract ORD and CD measurements on α- and β-phenylethylamines and a cyclic analogue possessing the benzoquinolizidine structure indicate that the absolute configuration of the asymmetric center may be assigned from the ORD curve. Compounds of S-configuration exhibit a positive multiple Cotton effect between 270 and 250 mμ.

Amine-N-oxide rearrangements : Mechanism and products of thermolysis☆

Abstract The thermolysis of a series of structurally similar amine-N-oxides has been examined individually and as mixtures. Product analysis shows that in addition to the expected N-alkoxylamines, smaller amounts of t-amines, aldehydes, and bibenzyls are formed. Thermolysis of mixtures produces intermolecular rearrangement products thus challenging the previously favored intramolecular mechanism as the exclusive process for the Meisenheimer rearrangement. The data are consistent with a mechanism involving homolytic fission to intermediates which recombine to produce the N-alkoxylamines.

The configuration and conformation of cularine

Abstract The absolute configuration of cularine has been shown to be d (= R) from the ORD of its hydrogenolysis product (VIII). The hydrochloride, methiodide and O-acetate of VIII showed a complete reversal of the long-wavelength Cotton effect and CD maximum at 290 mμ, while the short-wavelength Cotton effects at 226 and 210 mμ remained unaffected. This reversal is attributed to steric hindrance to rotation of the 2′-substituted benzyl moiety. NMR spectra at 100 mc/s permit the assignment of one of the 3 possible bent conformations to cularine.

Optical rotatory dispersion and absolute configuration—V. : The absolute configuration of natural plasmalogen☆

PLAWALOGENS are a group of aldehydogenic substances widely distributed in nature in both the animal and plant kingdom. 4 Their chemical structure is that of a cl thus specific rotations of [aIn -8~6”s” and +6*25”@’ are recorded for I-alkenyl-3-glycerylphosphorylethanolamine, and -7*85”s6 and “less than 2°“2b for I-alkenyl-3glycerylphosphorylcholine. No optical rotations have been reported either for the l-alkenyl(III) or for the I-alkyl-glycerols (II) obtained by hydrolysis and hydrogenation of plasmalogens.

Optical rotatory dispersion and absolute configuration—VIII : Petaline and other benzyltetrahydroisoquinoline alkaloids

Abstract The ORD of benzyltetrahydroisoquinoline alkaloids shows three Cotton effects which have been correlated with the UV absorption, CD and absolute configuration of these compounds. The application of this method shows petaline to have the D(=R) configuration.

Evidence for the intermolecular nature of the Meisenheimer rearrangement of amine N-oxides

Thermolysis of mixtures of structurally similar amine N-oxides leads to intermolecular rearrangement products, thus calling into question the previously favoured intramolecular mechanism as the exclusive process for the Meisenheimer rearrangement; the results are consistent with a mechanism involving homolytic fission to intermediates which recombine to produce the N-alkoxy-amines.