No abstract

In order to establish the structural requirements for binding to the brain cannabinoid receptor (CB1), we have synthesized numerous fatty acid amides, ethanolamides, and some related simple derivatives and have determined their Ki values. A few alpha-methyl- or alpha, alpha-dimethylarachidonoylalkylamides were also examined. In the 20:4, n-6 series, the unsubstituted amide is inactive; N-monoalkylation, at least up to a branched pentyl group, leads to significant binding. N,N-Dialkylation, with or without hydroxylation on one of the alkyl groups, leads to elimination of activity. Hydroxylation of the N-monoalkyl group at the omega carbon atom retains activity. In the 20x, n-6 series, x has to be either 3 or 4; the presence of only two double bonds leads to inactivation. In the n-3 series, the limited data reported suggest that the derived ethanolamides are either inactive or less active than comparable compounds in the n-6 series. Alkylation or dialkylation of the alpha carbon adjacent to the carbonyl group retains the level of binding in the case of anandamide (compounds 48, 49); however, alpha-monomethylation or alpha,alpha-dimethylation of N-propyl derivatives (50-53) potentiates binding and leads to the most active compounds seen in the present work (Ki values of 6.9 +/- 0.7 to 8.4 +/- 1.1 nM). We have confirmed that the presence of a chiral center on the N-alkyl substituent may lead to enantiomers which differ in their levels of binding (compounds 54, 57 and 55, 56).

The 1,1-dimethylheptyl (DMH) homologue of 7-hydroxy-delta 6-tetrahydrocannabinol (3) is the most potent cannabimimetic substance reported so far. Hydrogenation of 3 leads to a mixture of the epimers of 5'-(1,1-dimethylheptyl)-7-hydroxyhexahydrocannabinol or to either the equatorial (7) or to the axial epimer (8), depending on the catalysts and conditions used. Compound 7 discriminates for delta 1-THC (2) in pigeons (ED50 = 0.002 mg/kg, after 4.5 h), at the potency level of 3, and binds to the cannabinoid receptor with a KD of 45 pM, considerably lower than the Ki of 180 pM measured for compound 3 and the Ki of 2.0 nM measured for CP-55940 (1), a widely employed ligand. Tritiated 7 was used as a novel probe for the cannabinoid receptor.

No abstract

No abstract

In this review we present a summary of recent results on the action of cannabinoids endogenous to the central nervous system (CNS; the anandamides) and peripheral tissues (2-arachidonoyl-glycerol 2-Ara-GI), as well as two synthetic cannabinoids, HU-2 10, a highly potent cannabinoid agonist, and its enantiomer, HU-2 1 I , an N-methyl-D-aspartate (NMDA) antagonist that lacks cannabinoid activity.The major psychoactive constituent of Cannabis sativa, A9-tetrahydrocannabinol (THC), was first isolated in pure form and its structure elucidated by our group in 1964 (49). Shortly thereafter, its stereochemistry was established ( Fig. 1) (80), and several total syntheses were achieved (79,102). These advances and the public interest in Cannabis, in particular during the "flower years" of the 1960s and 197Os, led to extensive research that clarified to a large extent many aspects of cannabinoid action such as its metabolism, physiological and pharmacological effects, and various clinical and therapeutic aspects (28,74,85,99). It was not until 1988, however, that a major breakthrough in our understanding of the mode of action of cannabinoids was achieved with the identification and, shortly thereafter the cloning, of a cannabinoid receptor (now designated CB,) in brain and in neuroblastoma cells (25,76). In 1993 a second receptor (CB2) was found to be present in spleen (88). Various structural and biochemical aspects of CBI and CB2 have been reviewed in a recent book (98) and in detailed reviews (31,57,75). While CBI is found mostly in the brain, its RNA has also been detected in some peripheral tissues (21,2930). CB2 and its RNA have been detected only in cells of the immune system (39,88).

The aim of this work was to develop alternative peptideloaded microspheres using liposphere formulationÐa lipid based microdispersion system. This formulation represents a new type of lipid or polymer-based encapsulation system developed for parenteral and topical drug delivery of bioactive compounds. Our strategy was to utilize the liposphere formulation to improve the entrapment efficiency and release profile of triptorelin and leuprolide [luteinizing hormone±releasing hormone (LHRH) analogues] in vitro. Peptides (2% w/w) were loaded into lipospheres contained of polylactic acid (PLA) or poly(lactic-co-glycolic acid) (PLGA) with several types of phospholipids. The effects of polymer and phospholipid type and concentration, method of preparation and solvents on the liposphere characteristics, particle size, surface and bulk structure, drug diffusion rate, and erosion rate of the polymeric matrix were studied. The use of L-PLA (M w = 2000) and hydrogenated soybean phosphatidylcholine (HSPC) with phospholipid±polymer ratio of 1 : 6 w/w, was the most efficient composition that formed lipospheres of particle size in the range of 10 mm with most of the phospholipid embedded on the particles surface. In a typical procedure, peptides were dissolved in N-methyl-2-pyrrolidone (NMP), and dispersed in a solution of polymer and phospholipids in a mixture of NMP and chloroform with the use of 0.1% poly(vinyl alcohol) (PVA) as the emulsified aqueous medium. Uniform microspheres were prepared after solution was mixed at 2000 rpm at room temperature for 30 min. Using this formulation, the entrapment efficiency of LHRH analogues in lipospheres was up to 80%, and the peptides were released for more than 30 days.

This study demonstrates the promise of anhydride prodrugs for extending drug action and shielding the carboxylic acid group.