Browsing by Author "Howard, Patrick Yeager"
Now showing 1 - 2 of 2
- Results Per Page
- Sort Options
Item Synthetic dipeptides and their application to the resolution of amino acid enantiomers(1971) Howard, Patrick Yeager; Parr, Wolfgang; Bear, John L.; Oró, John F.; Cominsky, N. Catherine; Zlatkis, AlbertThe synthesis of six N-TFA-L-L-dipeptide cyclohexyl esters has been successfully completed. N-trifluoroacetyl (TFA) dipeptide cyclohexyl esters of L-alanyl-L-alanine, L-a-amino-p-butyryl-L-a-amino-n-butyric acid, L-norvalyl-L-norvaline, L-leucyl-L-leucine, L-isoleucyl-L-isoleucine and L-norleucyl-L-norleucine have been made by coupling their tert- butoxycarbonyl-L-amino acid hydroxybenztriazolates with L-amino acid cyclohexyl esters. The behavior of these di peptides as optically active stationary phases for the gas-liquid chromatographic separation of N-TFA-D,L-amino acid isopropyl esters has been examined with respect to separation factors and differential thermodynamic properties of solution. An increase in size of the alkyl substituents on the asymmetric centers of the di peptide solvent produces greater solute-solvent interaction. However, the same modification, when applied to the side chain on the a carbon of the solute, causes a decrease in interaction. Each phase has been investigated with respect to complete separability for a mixture of naturally occurring enantiomeric amino acid derivatives; and N-TFA-L-[alpha]-amino-n-butyryl-L-[alpha]-amino-n-butyric acid cyclohexyl ester has been found to effect total resolution of the different amino acids as well as their respective enantiomers. Another of the di peptides, N-TFA-L-norvalyl-L-norvaline cyclohexyl ester, shows complete separation for D,L isomers of a tert-leucine derivative--an amino acid for which complete resolution of its D and L forms by gas-liquid chromatography has not been previously achieved.Item The thermal isomerization of [alpha]-pinene(1970) Howard, Patrick Yeager; Willcott, Mark Robert; Fitzgerald, J. M.; Cominsky, N. C.; McElrath, Eby N.The kinetic and thermodynamic properties of the thermal isomerization of [alpha]-pinene have been examined. A stereospecifically deuterated [alpha]-pinene was synthesized and pyrolyzed. The positions of the label in the products were determined, and this information was used in formulating a mechanism for the pinene rearrangements. Arrhenius expressions for the thermal rearrangement of [alpha]-pinene to dipentene and alloocimene have been determined for rate data obtained from a stirred flow reactor. The new rates have been compared, in detail, to those determined in earlier studies and found to be similar, but not identical. The pinene reaction is unimolecular and produces dipentene and alloocimene as primary products. It is not possible to construct a completely detailed mechanism from a review of all the available data. It has been found that the two primary products are not formed in two simultaneous independent reactions. The report that pinene undergoes a thermal racemization has been disproved for temperatures less than 275[degrees]C.