We describe a synthetic ligand, "DAKLI" (Dynorphin A-analogue Kappa LIgand), related to the opioid peptide dynorphin A. A single reactive amino group at the extended carboxyl terminus permits various reporter groups to be attached, such as '25I-labeled Bolton-Hunter reagent, fluorescein isothiocyanate, or biotin. These derivatives have high affinity and selectivity for the dynorphin (I opioid) receptor. An incidental finding is that untreated guinea pig brain membranes have saturable avidin binding sites.To label one type of receptor binding site in the presence of related types, a radioligand should (i) have very high affinity for the site to be labeled, (ii) be highly selective for that site, (iii) have high enough specific radioactivity to be usable at a low concentration to maximize its binding at the preferred site relative to that at the next-preferred site, (iv) for convenience incorporate a radioisotope such as 125I with a high-energy mode of decay.Dynorphin A (Tyr-Gly-Gly-Phe-Leu-Arg-Arg-Ile-Arg-ProLys-Leu-Lys-Trp-Asp-Asn-Gln) is a 17-residue endogenous opioid peptide with selectivity for the K opioid receptor (1-3). Dynorphin A-(1-13) is as potent and as selective for the K binding site as is the natural full-length peptide (4), so we surmised that this fragment could be modified safely by extension at the C terminus. For flexibility of functionalization with various reporter groups, we used a primary amino function at the C terminus as a handle. Lysine-11 and lysine-13 (especially the former) play essential roles in determining K affinity and selectivity (5). To abolish the reactive E-amino groups, yet retain the charges at these two positions, we replaced lysine with arginine. Our C-terminal extension consisted of glycine-14, followed by 1,5-diaminopentane. The resulting peptide is called "DAKLI" (Dynor-After synthesis of the peptide by the solid-phase method and its removal from the resin by aminolysis with 1,5-diaminopentane, the free a-amino group of tyrosine-1 remains blocked by the t-butoxycarbonyl (Boc) group and the only reactive amine is at the extended C terminus. This feature allows the facile production, from [Boc] 25 -22°(c 0.4, AcOH). Reversed-phase analytical HPLC (as above but 4 x 250 mm; particle size, 5 ,um; gradient, 10-50% CH3CN; 0.03 M in NH4OAc, pH 4.5; A = 280 nm) showed the product to be 90% pure, and the amino acid analysis after 6 M HCl hydrolysis (18 hr, 110°C) gave ratios in accord with the desired structure: Pro, 1.1 (1); Gly, 2.9 (3); Ile, 0.9 (1); Leu, 2.0 (2); Tyr, 1.3 (1); Phe, 1.1 (1); Arg, 4.9 (5). The expected amino acid sequence was obtained on an Applied Biosystems (Foster City, CA) 470A microsequencer (K. Jarnagin, Syntex Research).Preparation of lodinated Peptides DAKLII and DAKLII**. BH (Sigma) was iodinated by the chloramine-T method as follows: to 5 mg of dry BH was added 50 mg of NaI in 40 ,ul of 50 mM sodium phosphate buffer, followed immediately by 0.5 ml of chloramine T (30 mg/ml in 250 mM sodium phosphate buffer). The reaction was terminate...

Donepezil, a cholinesterase inhibitor with good central nervous system penetration, has been crystallized as a tertiary amine salt with a disordered oxalate anion to give the title compound, (R,S)-1-benzyl-4-[(5,6-dimethoxy-1-oxoindan-2-yl)methyl]piperidinium hydrogen oxalate trihydrate, C24H30NO3+.C2HO4-.3H2O. The indanone and piperidine ring planes are inclined at an angle of 33.4 (1) degrees. A comparison is made with the piperidinium cation bound in acetylcholinesterase in the solid state. The methylene units bridging the indanone-piperidine-benzyl groups determine the molecular shape and conformational features. The structure is stabilized mainly by O-H...O and N-H...O hydrogen bonds, with water molecules mediating interactions between oxalate anions and donepezilium cations.

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Dextrorphan (+)-tartrate, purified by repeated crystallization to remove all traces of the enantiomer levorphanol, binds to IL, 6, and K sites on guinea-pig brain membranes with lower affinities (by a factor of 400-3200) than levorphanol. In the guinea-pig ileum myenteric plexus longitudinal muscle preparation (GPI), dextrorphan, at 100-200 ,uM, inhibits the electrically stimulated twitch, but this action is not blocked or reversed by naloxone; both (+)-and (-)-naloxone produce similar non-opioid twitch inhibition at comparable concentrations. At 10-20 jaM, dextrorphan' blocks and reverses the twitch inhibition due to ,u and KWagonists, but the blockade can be overcome only partially by increasing the agonist concentration. We conclude that dextrorphan is an