Cannabinoid receptor 2 (CB2R)-dependent signaling is implicated in neuronal physiology and immune surveillance by brain microglia. Selective CB2R agonists hold therapeutic promise for inflammatory and other neurological disorders. Information on human CB2R (hCB2R) ligand-binding and functional domains is needed to inform the rational design and optimization of candidate druglike hCB2R agonists. Prior demonstration that hCB2R transmembrane helix 2 (TMH2) cysteine C2.59(89) reacts with small-molecule methanethiosulfonates showed that this cysteine residue is accessible to sulfhydryl derivatization reagents. We now report the design and application of two novel, pharmacologically active, high-affinity molecular probes, AM4073 and AM4099, as chemical reporters to interrogate directly the interaction of classical cannabinoid agonists with hCB2R cysteine residues. AM4073 has one electrophilic isothiocyanate (NCS) functionality at the C9 position of its cyclohexenyl C-ring, whereas AM4099 has NCS groups at that position and at the terminus of its aromatic A-ring C3 side chain. Pretreatment of wild-type hCB2R with either probe reduced subsequent [3H]CP55,940 specific binding by ∼60%. Conservative serine substitution of any hCB2R TMH cysteine residue except C2.59(89) did not affect the reduction of [3H]CP55,940 specific binding by either probe, suggesting that AM4073 and AM4099 interact irreversibly with this TMH2 cysteine. In contrast, AM841, an exceptionally potent hCB2R megagonist and direct AM4073/4099 congener bearing a single electrophilic NCS group at the terminus of its C3 side chain, had been demonstrated to bind covalently to TMH6 cysteine C6.47(257) and not C2.59(89). Molecular modeling indicates that the AM4073-hCB2R* interaction at C2.59(89) orients this classical cannabinoid away from TMH6 and toward the TMH2-TMH3 interface in the receptor's hydrophobic binding pocket, whereas the AM841-hCB2R* interaction at C6.47(257) favors agonist orientation toward TMH6/7. These data constitute initial evidence that TMH2 cysteine C2.59(89) is a component of the hCB2R binding pocket for classical cannabinoids. The results further demonstrate how interactions between classical cannabinoids and specific amino acids within the hCB2R* ligand-binding domain act as determinants of agonist pharmacological properties and the architecture of the agonist-hCB2R* conformational ensemble, allowing the receptor to adopt distinct activity states, such that interaction of classical cannabinoids with TMH6 cysteine C6.47(257) favors a binding pose more advantageous for agonist potency than does their interaction with TMH2 cysteine C2.59(89).

The aliphatic side chain plays a pivotal role in determining the cannabinergic potency of tricyclic classical cannabinoids, and we have previously shown that this chain could be substituted successfully by adamantyl or other polycyclic groups. In an effort to explore the pharmacophoric features of these conformationally fixed groups, we have synthesized a series of analogues in which the C3 position is substituted directly with an adamantyl group bearing functionality at one of the tertiary carbon atoms. These substituents included the electrophilic isothiocyanate and photoactivatable azido groups, both of which are capable of covalent attachment with the target protein. Our results show that substitution at the 3'-adamantyl position can lead to ligands with improved affinities and CB1/CB2 selectivities. Our work has also led to the development of two successful covalent probes with high affinities for both cannabinoid receptors, namely, the electrophilic isothiocyanate AM994 and the photoactivatable aliphatic azido AM993 analogues.

The “subjective high” from marijuana ingestion is likely due to Δ9-tetrahydrocannabinol (THC) activating the central cannabinoid receptor type 1 (CB1R) of the endocannabinoid signaling system. THC is a weak partial agonist according to in vitro assays, yet THC mimics the behavioral effects induced by more efficacious cannabinergics. This distinction may be important for understanding similarities and differences in the dose–effect spectra produced by marijuana/THC and designer cannabimimetics (“synthetic marijuana”).

We report an approach for obtaining novel cannabinoid analogues with controllable deactivation and improved druggability. Our design involves the incorporation of a metabolically labile ester group at the 2'-position on a series of (-)-Δ(8)-THC analogues. We have sought to introduce benzylic substituents α to the ester group which affect the half-lives of deactivation through enzymatic activity while enhancing the affinities and efficacies of individual ligands for the CB1 and CB2 receptors. The 1'-(S)-methyl, 1'-gem-dimethyl, and 1'-cyclobutyl analogues exhibit remarkably high affinities for both CB receptors. The novel ligands are susceptible to enzymatic hydrolysis by plasma esterases in a controllable manner, while their metabolites are inactive at the CB receptors. In further in vitro and in vivo experiments key analogues were shown to be potent CB1 receptor agonists and to exhibit CB1-mediated hypothermic and analgesic effects.

In pursuit of a more detailed understanding of the structural requirements for the key side chain cannabinoid pharmacophore, we have extended our SAR to cover a variety of conformationally modified side chains within the 9-keto and 9-hydroxyl tricyclic structures. Of the compounds described here, those with a seven-atom long side chain substituted with a cyclopentyl ring at C1' position have very high affinities for both CB1 and CB2 (0.97 nM < K(i) < 5.25 nM), with no preference for either of the two receptors. However, presence of the smaller cyclobutyl group at the C1' position leads to an optimal affinity and selectivity interaction with CB1. Thus, two of the C1'-cyclobutyl analogues, namely, (6aR,10aR)-3-(1-hexyl-cyclobut-1-yl)-6,6a,7,8,10,10a-hexahydro-1-hydroxy-6,6-dimethyl-9H-dibenzo[b,d]pyran-9-one and (6aR,9R,10aR)-3-(1-hexyl-cyclobut-1-yl)-6a,7,8,9,10,10a-hexahydro-6,6-dimethyl-6H-dibenzo[b,d]pyran-1,9 diol (7e-β, AM2389), exhibited remarkably high affinities (0.84 and 0.16 nM, respectively) and significant selectivities (16- and 26-fold, respectively) for CB1. Compound 7e-β was found to exhibit exceptionally high in vitro and in vivo potency with a relatively long duration of action.

N-Arachidonoyl ethanolamide or anandamide is an endocannabinoid found in most tissues where it acts as an important signaling mediator in a number of physiological and pathophysiological processes. Consequently, intense effort has been focused on understanding all its biosynthetic and metabolic pathways. Herein we report human alcohol dehydrogenase-catalyzed sequential oxidation of anandamide to N-arachidonoyl glycine, a prototypical member of the class of long chain fatty acyl glycines, a new group of lipid mediators with a wide array of physiological effects. We also present a straightforward synthesis for a series of N-acyl glycinals including N-arachidonoyl glycinal, an intermediate in the alcohol dehydrogenase-catalyzed oxidation of anandamide.

Ti(NMe2)4, when combined with [HNMe2Ph][B(C6F5)4], catalyzes carboamination of alkynes with aldimines to form highly arylated α,β-unsaturated imines with exclusive (E,E)-configuration at the olefin and imine residues. Complexes [Ti(NHMe2)(NMe2)3][B(C6F5)4] and [TiNAr(NHMe2)3(NMe2)][B(C6F5)4] (Ar = 2,6-iPr2C6H3), isolated from stoichiometric reactions involving Ti(NMe2)4/[HNMe2Ph][B(C6F5)4] and Ti(NMe2)4/[HNMe2Ph][B(C6F5)4]/ArNH2, respectively, also catalyze carboamination with activity comparable to that of the Ti(NMe2)4/[HNMe2Ph][B(C6F5)4] system.

Alpha-hydrogen abstraction and alpha-hydrogen migration reactions yield novel titanium(IV) complexes bearing terminal phosphinidene ligands. Via an alpha-H migration reaction, the phosphinidene ((tBu)nacnac)Ti=P[Trip](CH(2)(tBu) ((tBu)nacnac(-) = [Ar]NC((t)Bu)CHC((t)Bu)N[Ar], Ar = 2,6-(CHMe2)(2C6H3, Trip = 2,4,6-(i)Pr3C6H2) was prepared by the addition of the primary phosphide LiPH[Trip] to the nucleophilic alkylidene triflato complex ((tBu)nacnac)Ti=CH(t)Bu(OTf), while alpha-H abstraction was promoted by the addition of LiPH[Trip] to the dimethyl triflato precursor ((tBu)nacnac)Ti(CH)(2)(OTf) to afford ((tBu)nacnac)Ti=P[Trip](CH3). Treatment of ((tBu)nacnac)Ti=P[Trip](CH3) with B(C6F5)(3) induces methide abstraction concurrent with formation of the first titanium(IV) phosphinidene zwitterion complex ((tBu)nacnac)Ti=P[Trip]{CH3B(C6F5)(3)}. Complex ((tBu)nacnac)Ti=P[Trip]{CH3B(C6F5)(3)} [2 + 2] cycloadds readily PhCCPh to afford the phosphametallacyclobutene [((tBu)nacnac)Ti(P[Trip]PhCCPh)][CH3B(C6F5)(3)]. These titanium(IV) phosphinidene complexes possess the shortest Ti=P bonds reported, have linear phosphinidene groups, and reveal significantly upfielded solution 31P NMR spectroscopic resonances for the phosphinidene phosphorus. Solid state 31P NMR spectroscopic data also corroborate with all three complexes possessing considerably shielded chemical shifts for the linear and terminal phosphinidene functionality. In addition, high-level DFT studies on the phosphinidenes suggest the terminal phosphinidene linkage to be stabilized via a pseudo Ti[triple bond]P bond. Linearity about the Ti-P-C(ipso) linkage is highly dependent on the sterically encumbering substituents protecting the phosphinidene. Complex ((tBu)nacnac)Ti=P[Trip]{CH3B(C6F5))(3)} can catalyze the hydrophosphination of PhCCPh with H(2)PPh to produce the secondary vinylphosphine HP[Ph]PhC=CHPh. In addition, we demonstrate that this zwitterion is a powerful phospha-Staudinger reagent and can therefore act as a carboamination precatalyst of diphenylacetylene with aldimines.

Hypothiocyanite (OSCN-) plays an important role in the human host defense system as a nonimmunological antimicrobial agent. Although many conjugate reactions of proteins have been attributed to OSCN-, there is little precedence for such reactions in small-molecule chemistry. We will discuss the derivative species that are in equilibrium with OSCN-, including hypothiocyanous acid (HOSCN), thiocyanogen [(SCN)(2)], and trighiocyanate [(SCN)(3)(-)], the first organic derivatives of this mixture to be fully characterized, and we will describe a new method of synthesizing hypothiocyanite.

The catalyst system Pt(DVDS)/P((BuNCH2CH2)-Bu-i)(3)N (DVDS = [(H2C=CH)Me2Si](2)O), containing a bulky aminophosphine ligand, catalyzes the hydrosilylation of terminal alkynes possessing a variety of functional groups using Ph3SiH or Et3SiH. These reactions occur stereo- and regioselectively to give beta-(E)-vinylsilanes with 97-99% selectivity in 76-98% yield. Using Pt-2(DVDS)(3), this selectivity ranged from 63 to 93%, except in one case, where the selectivities were the same for both catalyst systems.

Sulfenyl thiocyanate (RSSCN) derivatives of penicillamine (PENSCN) and glutathione (GSSCN) have been synthesized in situ at pH = 0 from equilibrium mixtures that consists of hypothiocyanous acid (HOSCN), thiocyanogen ((SCN)2), and trithiocyanate ((SCN)3-). The electrophilic thiocyanating agent N-thiocyanatosuccinimide (NTS) also reacts with PEN and GSH to yield the corresponding RSSCN derivatives. PENSCN and GSSCN were characterized by NMR, ES-MS, and IR spectroscopy. While stable at pH = 0, at higher pH the RSSCN derivatives decompose to give products that are consistent with hydrolysis and formation of reactive sulfenic acids.

The coordinatively unsaturated complex [Cp*Ru((PMePr2)-Pr-i)(2)][BAr'(4)] (1; BAr'(4) = B{3,5-C6H3(CF3)(2)}(4)) reacts with 1-alkynes in diethyl ether at 0 degreesC, furnishing the Ru-IV alkynyl hydrido derivatives [Cp*RuH(Cequivalent toCR)((PMePr2)-Pr-i)(2)] [BAr'(4)]. In an analogous fashion, the reaction of I with 1-alkyn-3-ols in diethyl ether at 0 degreesC leads to the 3-hydroxyalkynyl hydrido complexes [Cp*RuH(Cequivalent toCC(OH)RR')((PMePr2)-Pr-i)(2)][BAr'(4)]. The complexes [Cp*RuH(Cequivalent toCCOOMe)((PMePr2)-Pr-i)(2)][BAr'(4)] and [Cp*RuH(Cequivalent toCC(OH)Ph-2)((PMePr2)-Pr-i)(2)][BAr'(4)].Et2O have been structurally characterized, and their crystal structures show a transoid disposition of the hydride and alkynyl ligands. These compounds are stereochemically nonrigid and undergo a rapid equilibrium between possible stereoisomers in solution, which has been studied by variable-temperature NMR spectroscopy and computer simulation. The dynamic NMR study for these processes indicates energy barriers of ca. 11 kcal mol(-1), and moreover the differences in energy for the possible stereoisomers are very small (ca. 1 kcal mol(-1)). The alkynyl hydrido complexes rearrange to their more stable vinylidene or hydroxyvinylidene, tautomers. Spontaneous dehydration of the latter leads to either vinylvinylidene or allenylidene complexes.

The reaction of [Cp*RuCl(dppm)] with NaBAr'4 in fluorobenzene under argon generates the binuclear complex [{Cp*Ru}2(μ-Cl)(μ-dppm)2][BAr'4], which has been structurally characterized. No complex was isolated from the reaction of [Cp*RuCl(dppe)] with NaBAr'4 under argon, but halide abstraction from [Cp*RuCl(PP)] (PP = dppm, dppe) under dinitrogen using NaBAr'4 yielded the corresponding cationic terminal dinitrogen complexes [Cp*Ru(N2)(PP)][BAr'4].

A number of 16e two-legged piano-stool complexes [Cp*Ru(PP)] [BAr'(4)] have been prepared by reaction of NaBAr'(4) with either [CP*RuCl(PP)] (PP = (PEt3)(2), (Pr2PCH2CH2PPr2)-Pr-i-Pr-i (dippe), (PPh3)(2)) or [Cp*RuCl(PR3)] plus PR3 (PR3 = (PMePr2)-Pr-i, (PPhPr2)-Pr-i) in fluorobenzene under argon. The complexes [Cp*Ru(PEt3)(2)] [BAr'(4)], [Cp*Ru(dippe)] [BAr'(4)], and [Cp*Ru(PMeiPr(2))(2)] [BAr'(4)] have been structurally characterized by X-ray crystallography. Attempts to isolate analogous species containing other phosphine ligands such as (PPr3)-Pr-i, PCy3, and PMe3 led to the sandwich derivative [CP*Ru(eta(6)-FPh)] [BAr'(4)], which was also structurally characterized. Both [CP*Ru-(PPh3)(2)] [BAr'(4)] and [Cp*Ru((PPhPr2)-Pr-i)(2)] [BAr'(4)] are unstable and rearrange to the 18e sandwich species [Cp*Ru(eta(6)-C6H5PR2)] [BAr'(4)] and to [Cp*Ru(eta(6)-C6H5POR2)][BAr'(4)] (R = Ph, Pr-i) under trace amounts of oxygen. The geometry of the 16e complexes as well as their affinity for an additional ligand depend on the substituents on the phosphorus. The reactivity with respect to the addition of N-2, PR3, O-2, H-2, and HCl to form 18e derivatives has been studied. Some model systems have been analyzed using density functional theory (DFT) calculations. Also included are comparative studies on the NN counterparts. The moieties [CpRu(PP)](+) (PP = (PH3)(2), H2PCH2CH2PH2) adopt typically pyramidal structures (i.e. in the absence of bulky and rigid substituents on P) versus planar structures of [CpRu(NN)](+) (NN = (NH3)(2), H2NCH2CH2NH2). [CpRu(PP)](+) is more stable but has nevertheless a higher affinity of adding a a ligand than [Cp*Ru(NN)](+).

The reaction of [CpRuCl(P)(2)] [(P)(2) = dippe (1,2-bis(diisopropylphosphino)ethane; (PEt3)(2); ((PMePr2)-Pr-i)(2)] with Na[BAr'(4)] (Ar'(4) = 3,5-bis(trifluoromethyl)phonyl) in fluorobenzene under argon generates the corresponding cationic 16-electron species [CpRu(P)(2)](+), which reacts with trace amounts of dinitrogen present even in high-purity argon furnishing the dinitrogen-bridged complexes [{CpRu(P)(2)}(2)(mu-N-2)][BAr'(4)](2) [(P)(2) = dippe 1a; (PEt3)(2) 1b; ((PMePr2)-Pr-i)(2) 1c]. If the reaction is performed under dinitrogen, the terminal dinitrogen complexes [CpRu(N-2)(P)(2)] [BAr'(4)] [(P)(2) = dippe 2a; ((PMePr2)-Pr-i)(2) 2c] are obtained. Compound 1b was obtained irrespectively of the atmosphere used, and no terminal dinitrogen complex has been detected. The crystal structures of 1 a, 1b, and 2a have been determined. During one attempt to isolate the 16-electron complex [CpRu(PMeiPr2)(2)] [BA'(4)], the 18-electron tris(phosphine) derivative [CpRu((PMePr2)-Pr-i)(3)][BAr'(4)], 3, was obtained instead, and it was structurally characterized. Halide abstraction from [CpRuCl((PMePr2)-Pr-i)(PPh3)] under dinitrogen using Na[BAr'(4)] yielded [CpRu(N-2)((PMePr2)-Pr-i)(PPh3)] [BAr'(4)], 2d, but under argon the complex [CpRu((PMePr2)-Pr-i)(PPh3)]-[BAr'(4)], 4, which contains a rare eta(3)-coordinated PPh3 ligand as shown by X-ray crystallography, was isolated.

Reaction of NaBH4 with [Cp*RuCl2(EPh3)] (E=Sb 1a, As 1b) in THF/EtOH affords the trihydride complexes [Cp*RuH3(EPh3)] (E=Sb 2a, As 2b) in good yield. These trihydrides are protonated by HBF4·OEt2 in CH2Cl2 at −80°C furnishing the cationic bis(dihydrogen) complexes [Cp*Ru(H2)2(EPh3)][BF4] (E=Sb 3a, As 3b), which were characterized in solution by T1 and 1JHD measurements. These species are unstable and decompose at T>0°C. The reaction of [Cp*RuCl(SbPh3)2] with H2 and NaBAr′4 in fluorobenzene yields the dihydride [Cp*RuH2(SbPh3)2][BAr′4] (5). Protonation of the monohydride [Cp*RuH(SbPh3)2] (6) by HBF4·OEt2 in CH2Cl2 at −80°C generates the dihydrogen complex [Cp*Ru(H2)(SbPh3)2]+ (7), which rearranges to its dihydride tautomer 5 when the temperature is raised.

Dinuclear di(mu-alkoxo) bridged [Fe2L21] 1 (L-1 = trianion of 1,3-bis(salicylideneamino)propan-2-ol) and [Fe2L22] 2 (L-2 = trianion of 1,3-bis(salicylamino)propan-2-ol) and di(mu-phenoxo) bridged [Fe2L23] 3 (L-3 = trianion of 4-methyl-2,6-bis(salicylideneaminomethyl)phenol) and [Fe2L24] 4 (L-4 = trianion of 4-methyl-2,6-bis(salicylaminomethyl)phenol) complexes have been synthesized and characterized. The crystal structure of 1 contains two molecules in the asymmetric unit and each molecule has two FeN2O4 distorted octahedral co-ordination units. The structure of 2 consists of a centrosymmetric dimer where the two crystallographically equivalent metal ions are asymmetrically bridged by two alkoxo oxygen atoms. The iron(III) centers have N2O4 co-ordination cores with amine nitrogens and phenolate oxygens in cis position. The crystal structure of 3 contains trans-FeN2O4 distorted octahedral co-ordination units bridged by two phenoxo oxygen atoms. The electronic spectra of all the complexes are characterized by high intensity charge-transfer transitions. Cyclic voltammetric studies of 1, 3 and 4 in dichloromethane solvent reveal stepwise reduction of (FeFeIII)-Fe-III to mixed-valence (FeFeII)-Fe-III and reduced (FeFeII)-Fe-II species while 2 exhibits a single quasireversible reduction peak corresponding to the mixed-valence form.