In order to develop novel κ agonists restricted to the periphery, a diastereo- and enantioselective synthesis of (4aR,5S,8aS)-configured decahydroquinoxalines 5-8 was developed. Physicochemical and pharmacological properties were fine-tuned by structural modifications in the arylacetamide and amine part of the pharmacophore as well as in the amine part outside the pharmacophore. The decahydroquinoxalines 5-8 show single-digit nanomolar to subnanomolar κ-opioid receptor affinity, full κ agonistic activity in the [S]GTPγS assay, and high selectivity over μ, δ, σ, and σ receptors as well as the PCP binding site of the NMDA receptor. Several analogues were selective for the periphery. The anti-inflammatory activity of 5-8 after topical application was investigated in two mouse models of dermatitis. The methanesulfonamide 8a containing the (S)-configured hydroxypyrrolidine ring was identified as a potent (K = 0.63 nM) and highly selective κ agonist (EC = 1.8 nM) selective for the periphery with dose-dependent anti-inflammatory activity in acute and chronic skin inflammation.

Keywords: Asymmetric catalysis / Ligand design / Bisoxazoline ligands / Non-proteinogenic amino acids / Chiral Lewis acidsThe steric influence of extended aryl substituents on 2,2Ј-bis(1,3-oxazoline) ligands was investigated in a series of asymmetric catalytic reactions such as Mukaiyama aldol and Michael reactions, hetero-Diels-Alder processes, and allylic alkylation reactions. 4,4Ј-(2-Naphthyl)-and 4,4Ј-(9-anthryl)-

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A chemoenzymatic approach to the synthesis of functionalized a-methyl a-substituted amino acids is detailed. This involves amidasemediated enzymatic resolution of a-methyl a-substituted side-chain w-unsaturated amino acids followed by functionalization via cross-metathesis.Keywords: amino amidase; cross-metathesis; enzyme catalysis; a-methyl a-substituted amino acids; side-chain w-unsaturated a-amino acids Enantiomerically pure a,a-disubstituted a-amino acids, especially a-methyl a-substituted amino acids, are of increasing interest for the agrochemical and pharmaceutical industry.[1] Compared to their a-H counterparts, peptides containing one or more such amino acids are less prone to epimerization, display enhanced metabolic stability and possess different folding behavior.[2] In line with our research on metathesis applications of side-chain w-unsaturated a-Hamino acids, [3] and inspired by successful ring-closing metathesis examples of a-methyl a-substituted amino acids from our own [4] and other groups, [5] we set out to explore the viability of a cross-metathesis [6] route to prepare functionalized a-methyl a-substituted amino acids. As a result, we herewith report that by combining enzymatic resolution of the racemic a,adisubstituted side-chain w-unsaturated amino acid amides 3 [4,7] with subsequent cross-metathesis on the terminal olefin functions, the functionalized a-amino acids 1 are readily accessible (Scheme 1). Although we will not discuss any follow-up chemistry of the functionality introduced in the final products, it will be clear that the resulting functional group provides ample opportunity for further synthetic derivatization.[8]Enantiopure a-methyl a-allylglycine amide (R)-7 and the corresponding acid (S)-10 were synthesized previously in our lab via a chemoenzymatic strategy. [4,7] The synthesis of the homologous a-amino acids 11 and 12 proceeded in a different manner as shown in Scheme 2, but also involved an enzymatic resolution to obtain the (S)-a-amino acids in enantiopure form. The strategy commenced with methyl acetoacetate (4), which via standard alkylation with the required olefin, hydroxide-mediated saponification and subsequent acidic decarboxylation was converted into ketones 5 and 6 in good overall yields. Subjection to Strecker conditions, followed by partial nitrile hydrolysis (NaOH, PhCHO, MeOH) and subsequent Schiff base hydrolysis (4 N HCl) provided the aamino acid amides 8 and 9 in good overall yields. They were made salt-free via extraction from a basic water layer (pH 10) with CH 2 Cl 2 and after concentration subjected to whole cells from Mycobacterium neoaurum ATCC 25795 in an aqueous solution starting at pH 8.3. After 18 h, the reaction mixtures were worked up, the products were separated and purified via ion exchange chromatography. Chiral HPLC analysis showed excellent ees for a-amino acids (S)-11 and (S)-12 of 99 and 98.5 %, respectively. These numScheme 1. Retrosynthesis of enantiopure side-chain w-unsaturated a-methyl a-amino acids.

A Cross-Metathesis Route to Functionalized α-Methyl α-Substituted Amino Acids. -The enzymatic resolution of racemic amides (I) followed by cross-metathesis on the terminal olefin functions affords the target compounds. -(STORCKEN, R. P. M.; PANELLA, L.; VAN DELFT, F. L.; KAPTEIN, B.; BROXTERMAN, Q. B.; SCHOEMAKER, H. E.; RUTJES*, F. P. J. T.; Adv. Synth. Catal. 349 (2007) 1-2, 161-164; Inst. Mol. Mater., Radboud Univ. Nijmegen, NL-6525 ED Nijmegen, Neth.; Eng.) -Klein 21-165