Paul W. Baures

An efficient asymmetric synthesis of substituted phenyl glycidic esters

Abstract Chiral substituted glycidic esters have been prepared from their corresponding chalcones via a two step procedure consisting of an asymmetric epoxidation mediated by a poly-L-leucine polymer, followed by a previously unreported Baeyer-Villiger oxidation. The regioselectivity of this latter procedure was found to depend on the aryl substituent.

An improved method of oxazolidinone hydrolysis in the asymmetric synthesis of α-alkylprolines

Abstract An improvement in Seebachs method for the synthesis of α-alkylprolines is reported wherein the hydrolysis of the chiral oxazolidinone 2 is performed on a suspension of silica gel in MeOH/H 2 O. Following hydrolysis, the pure α-alkylproline can be obtained by filtration thereby avoiding a tedious ion exchange purification.

Synthesis and dopamine receptor modulating activity of unsubstituted and substituted triproline analogues of L-prolyl-L-leucyl-glycinamide (PLG)

Triprolines Pro-Pro-Pro-NH2 (4), Pro-Pro-D-Pro-NH2 (5), Pro-Pro(trans-3-Me)-D-Pro-NH2 (6), and Pro-Pro(cis-3-Me)-D-Pro-NH2 (7) were made as conformationally constrained analogues of Pro-Leu-Gly-NH2. Triprolines 4-6 produced significant increases in the high- and low-affinity state ratio (RH/RL) of the dopamine receptor, but only 4 was found to increase apomorphine induced rotations in 6-hydroxydopamine-lesioned rats.

Solution and solid-state hydrogen bond patterns ofo-methoxy- ando-ethoxybenzoic acids

The hydrogen bond patterns ofo-alkoxybenzoic acids have been shown previously to involve intramolecular hydrogen bonds. In this paper we show thato-methoxybenzoic acid (I) and o-ethoxybenzoic acid (II) both exist as monomers with intramolecular hydrogen bonds in solution but that, in the solid-state,I crystallizes as hydrogen-bonded dimers whileII crystallizes with an intramolecular hydrogen bond. The correlation between solution and solid-state hydrogen bond patterns is made using solution and solid-state IR and NMR methods and by correlating the solid-state patterns with known X-ray crystal structures. The crystal structure ofI is reported here. Crystal data: monoclinicP21/n;a=7.002(2),b=14.945(9),c=7.719(4) Å,β=115.44(3)°,Z=4,V=729.4 Å3, andR=0.046 (1660 reflections).

Olivanic acid analogues. Part 10. X-Ray crystallographic study of the stereochemistry of some 7-heteroatom-substituted 7-acetyl-8-oxo-3-oxa-1-azabicyclo[4.2.0]octane-2-spirocyclohexanes: functional group control of the stereoselectivity of their reduction products using borohydride reagents

(6RS, 7SR)-7-Acetyl-7-azido-8-oxo-3-oxa-1-azabicyclo[4.2.0]octane-2-spirocyclohexane 3 was obtained by reaction of mesyl azide with the trans-ketone 2 in the presence of aqueous base, and the stereochemistry of its major sodium borohydride reduction product, (6RS,7SR,9SR)-7-azido-7-(1-hydroxyethyl)-8-oxo-3-oxa-1-azabicyclo[4.2.0]octane-2-spirocyclohexane 4, was determined by X-ray crystallography. X-Ray studies of the keto sulfide 17 and the chloro ketone 20 confirmed their (6RS,7SR) relative stereochemistry. Reduction of 17 gave the alcohol 18 also with (6RS,7SR,9SR) stereochemistry. In contrast, reduction of 20 with trialkylborohydride reagents gave the (6RS,7SR,9RS)-chloro alcohol 21, and a mechanism is proposed to account for this reversal of C-9 stereoselectivity.