Side Chain Methyl Substitution in the δ-Opioid Receptor Antagonist TIPP Has an Important Effect on the Activity Profile
摘要:
The delta-opioid antagonist H-Tyr-Tic-Phe-Phe-OH (TIPP-OH) or its C-terminal amide analogue was systematically modified topologically by substitution of each amino acid residue by all stereoisomers of the corresponding beta-methyl amino acid. The potency and selectivity (delta- vs mu- and kappa-opioid receptor) were evaluated by radioreceptor binding assays. Agonist or antagonist potency were assayed in the mouse vas deferens and in the guinea pig ileum. In the TIPP analogues containing L-beta-methyl amino acids the influence on delta-receptor affinity and on delta-antagonist potency is limited, the [(2S,3R)-beta-MePhe(3)]TIPP-OH analogue being among the most potent delta-antagonists reported. In the D-beta-methyl amino acid series, the [D-beta-MeTic(2)] analogues are delta-selective antagonists whereas [D-Tic(2)]TIPP-NH2 is a delta-agonist. NMR studies did not indicate any influence of the beta-methyl substituent on the conformation of the Tic residue. The [(2R,3S)-beta-MePhe(3)]TIPP-NH2 is a potent delta-agonist, its C-terminal carboxylic acid analogue being more delta-selective but displaying partial agonism in both the delta- and mu-bioassay. These results constitute further examples of a profound influence of beta-methyl substitution on the potency, selectivity, and signal transduction properties of a peptide.
A catalytic asymmetric hetero-Diels-Alder (HDA) reaction has been achieved through hydrogen-bond directed gamma-addition of olefinic azlactones to isatins. This methodology provides an efficient access to spirooxindole dihydropyranones in moderate to good yields and with excellent enantioselectivities.
Organocatalytic Asymmetric Hetero-Diels–Alder Reaction of in Situ Generated Dienes: Access to α,β-Unsaturated δ-Lactones Featuring CF<sub>3</sub>-Substituted Quaternary Stereocenter
作者:Harshit Joshi、Ankit Yadav、Arko Das、Vinod K. Singh
DOI:10.1021/acs.joc.9b03076
日期:2020.3.6
Chiral bifunctional urea-catalyzed asymmetric direct hetero-Diels-Alderreaction between alkylidene azlactone-derived dienes and trifluoromethyl aryl ketones is reported for the first time. The direct hetero-Diels-Alderreaction followed by ring opening results in densely functionalized α,β-unsaturated δ-lactones featuring a CF3-substituted quaternary stereocenter in high yields with excellent enantioselectivities
An asymmetric, phase-transfer-catalyzed vinylogous conjugate addition–vinylogous cyclization cascade of olefinic azlactones with 4-nitro-5-styrylisoxazoles is reported. In the presence of an l-tert-leucine-derived urea–quaternary ammonium salt as a bifunctional phase-transfer catalyst and KF, two series of valuable optically pure cyclohexenones featuring two and three stereocenters were obtained in