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In a continuing effort to elucidate the structure-activity relationships of the lead antagonist N-[2-(3,4-dimethylbenzyl)-3-pivaloyloxypropyl]-N'-[4-(methylsulfonylamino)benzyl]thiourea (1), the distances between the proposed four pharmacophores in 1 have been varied by insertion or deletion of one carbon to optimize their fit to the receptor. In addition, the acyloxy group of the C region was replaced with amide and N-hydroxy amide to identify the pharmacophoric importance of the ester group in the C2 region. The results indicated that the pharmacophoric arrangement of 1 was optimal for receptor binding affinity and antagonism, and the ester of the C2 region was significant for receptor binding. Among the derivatives, compound 19 showed distinct behavior with a 2-fold improvement in antagonism but a 13-fold reduction in binding affinity compared to 1. The partial separation of pharmacophoric requirements of these two assays has been noted before and compound 19 is thus selective for the calcium entry-linked receptor population. The conformational analysis of 1 generated three distinct conformers having different types of hydrophobic interactions, which will be utilized for exploring the active conformation of the VR1 ligand.

A series of chain-branched 1,3-dibenzylthiourea derivatives were synthesized, and tested their antagonist activity against vanilloid receptor 1. Chain-branching led to a significant change in the mode of action and the potency. ( R )-Methyl or ethyl-branched 1,3-dibenzylthiourea derivatives showed the most potent antagonist activity up to the IC 50 value of 0.05 μM which is 10-fold more potent than capsazepine.

The structural modifications on the B-region of the potent and high affinity vanilloid receptor (VR1) lead ligand N-(3-acyloxy-2-benzylpropyl)-N′-[4-(methylsulfonylamino)benzyl]thiourea were investigated by the replacement of the thiourea with diverse isosteric functional groups. Structure–activity analysis indicated that the A-region in this series was the primary factor in determining the agonistic/antagonistic activities regardless of the B-region. The NC-hydroxy thiourea analogues (12, 13) showed excellent analgesic activities in the acetic acid writhing assay compared to the parent thiourea analogues.

A novel non-vanilloid VR1 antagonist consisting of a new vanilloid equivalent exhibits excellent analgesic effects as well as highly potent antagonistic activities in both capsaicin single channel and calcium uptake assays. In addition, the structural requirement for the vanilloid equivalent of the potent VR1 antagonist has also been elucidated.

We previously described a series of N-(3-acyloxy-2-benzylpropyl) homovanillate and N'-(4-hydroxy-3-methoxybenzyl) thiourea derivatives that were potent VR1 agonists with high-affinities and excellent analgesic profiles. The design of these simplified RTX analogues was based on our RTX-derived pharmacophore model which incorporates the 4-hydroxy-3-methoxyphenyl (A-region), C(20)-ester (B-region), orthophenyl (C1-region) and C(3)-keto (C2-region) groups of RTX. For the purpose of optimizing the spatial arrangement of the four principal pharmacophores on the lead agonists (1-4), we have modified the distances in the parent C-region, 3-acyloxy-2-benzylpropyl groups, by lengthening or shortening one carbon to vary the distances between the pharmacophores. We find that two of the amides, 4 and 19, possess EC(50) values1 nM for induction of calcium influx in the VR1-CHO cells. As observed previously, the structure-activity relations for inhibition of RTX binding to VR1 and for induction of calcium uptake were distinct, presumably reflecting both intrinsic and methodological factors. In order to find the active conformation of VR1 ligands, the energy-minimized conformations of seven selected agonists were determined and the positions of their four pharmacophores were matched with those of five low energy RTX conformations. The rms values for the overlaps in the pharmacophores were calculated and correlated with the measured binding affinities (K(i)) and calcium influx (EC(50)) values. The binding affinities of the agonists correlated best with the RMS values derived from RTX conformation E (r(2)=0.92), predicting a model of the active conformation of RTX and related vanilloids for binding to VR1. Poorer correlation was obtained between any of the conformations and the EC(50) values for calcium influx.

The vanilloid receptor VR1 is a polymodal nociceptor sensitive to capsaicin, protons, and heat. Because VR1 represents an attractive therapeutic target for conditions ranging from long-term pain to bladder hyperreflexia, we and other groups have sought to develop novel ligands with enhanced potencies and novel pharmacological properties. Here, we characterize two compounds, N-[2-(3,4-dimethylbenzyl)-3-(pivaloyloxy)propyl]-N'-[4-(methylsulfonylamino)benzyl]thiourea (JYL827) and N-(4-tert-butylbenzyl)-N'-[3-methoxy-4-(methylsulfonylamino)benzyl]thiourea (JYL1511), that function as partial agonists for rat VR1 heterologously expressed in Chinese hamster ovary cells. Both compounds showed substantially enhanced potency, inhibiting [3H] resiniferatoxin binding with Ki values of 29.3 +/- 7.6 and 50.4 +/- 16.5 nM, respectively, compared with 1810 +/- 270 nM for capsaicin. The compounds showed different extents of partial agonism, 6.8 +/- 0.7% and 17.4 +/- 0.6%, respectively, and the expected corresponding degrees of partial antagonism (93.9 +/- 0.9 and 84.1 +/- 3.2%, respectively). Their IC50 values for antagonism of 45Ca2+ uptake in response to capsaicin were 67.3 +/- 24.9 nM and 3.4 +/- 0.5 nM, respectively. Protons, temperature, and protein kinase C all function as coactivators/modulators of rVR1. All enhanced the extent of partial agonism of JYL827 and JYL1511. Thus, at pH 5.5, for example, the extents of partial agonism increased to 54.9 +/- 2.5% and to 90.7 +/- 1.7%, respectively, relative to the response elicited by 300 nM capsaicin. The extents of partial antagonism decreased correspondingly. Compounds such as JYL827 and JYL1511 now permit exploration of the potential utility of partial agonists of rVR1 in animal models. Our results emphasize, moreover, the strong dependence of such partial agonists on other modulators of rVR1 and predict that their biological behavior will depend strongly on biological context.

The structures of N-hydroxylamides 1a and 1b, previously reported by Lee et al. in J. Med. Chem. 2001, 44, 4309-4312 as strong protein kinase C (PK-C) ligands, were incorrect and correspond instead to esters 2a and 2b, respectively. Here, we report the synthesis and complete characterization of 1a and 1b together with the associated biological activity in terms of PK-C binding affinity.

The ( R )-DAG-lactones ( 5 and 7E/Z ) are conformationally constrained diacylglycerol (DAG) analogs with high potency as protein kinase C (PKC) ligands. Here, we have prepared and characterized their one-carbon lengthened analogs ( 6 and 8E/Z ). The target compounds were synthesized from 1,2- O -isopropylidene D-xylose through a key intermediate, 4-C-hydroxyethyl-2,3-dideoxy-D-glyceropentono-1,4-lactone ( 13 ); they were evaluated as competitive ligands to displace bound [ 3 H]phorbol 12,13-dibutyrate (PDBU) from a recombinant single isozyme (PKC-α). The binding affinities of the synthesized compounds were K i = 2.623 μM for 6 , K i = 1.080 μM for 8Z and K i = 0.92 μM for 8E , which were ca. 27, 90, and 70 times less potent than the corresponding parent compounds ( 5, 7Z and 7E ). Molecular modeling indicated that the reduced binding affinity of the representative 3-alkylidene lactone 8Z , as compared to 7Z , may be explained by its poor fit in the sn-1 binding mode as well as by its entropic loss due to the relatively flexible hydroxyethyl group.

Twenty-seven N,N',N"-trisubstituted thiourea derivatives were prepared. Among them, 1-[3-(4'-hydroxy-3'-methoxy-phenyl)-propyl]-1,3-diphenethyl-thiourea (8l, IC(50)=0.32 microM), showed 2-fold higher antagonistic activity than that of capsazepine (3, IC(50)=0.65 microM) against the vanilloid receptor in a (45)Ca(2+)-influx assay.

The stereoselective synthesis of two new bis-γ-butyrolactones, constructed on a dioxaspiro[4.4]nonane template, was efficiently completed in 11 steps from L-xylose. One of two isomers (2a) showed good binding affinity towards protein kinase C.

Alpinia oxphylla Miquel, which belongs to the ginger family (Zingiberaceae), has been used in Oriental herbal medicine. Our recent studies have revealed that the methanolic extract of A. oxyphylla suppresses mouse skin tumor promotion and induces apoptosis in cultured human promyelocytic leukemia cells. In the present work, we have assessed effects of yakuchinone A and yakuchinone B, phenolic diarylheptanoids derived from A. oxyphylla, on 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced inflammation and epidermal ornithine decarboxylase (ODC) activity as well as on skin tumor promotion in female ICR mice. Thus, topical application of 2 or 6 micromol of the diarylheptanoids prior to each topical dose of TPA significantly ameliorated 7,12-dimethylbenz[a]anthracene-initiated mouse skin tumor formation. In parallel with suppression of tumor promotion, topically applied yakuchinone A and B markedly inhibited TPA-induced epidermal ODC activity and ODC mRNA expression. In another experiment, yakuchinone A and B reduced production of tumor necrosis factor-alpha in TPA-stimulated mouse skin. Furthermore, both compounds inhibited the TPA-induced expression of cyclooxygenase-2 at both transcriptional and translational levels. These findings indicate that pungent diarylheptanoids from A. oxyphylla Miquel have an antitumor promotional activity that might be related to their anti-inflammatory properties.

In order to improve the analgesic activity and pharmacokinetics of thioureas 2 and 3, which we previously developed as potent vanilloid receptor (VR) agonists, we prepared and characterized phenolic modifications of them and of their amide surrogates ( 7 , 8 ). The aminoethyl analogue of the amide template 13 was a potent analgesic with an EC 50 =0.96 μg/kg in the AA-induced writhing test and with better in vivo stability than the parent phenol.

Phorbol esters, the archetypical (PKC) activators, induce apoptosis in androgen-sensitive LNCaP prostate cancer cells. In this study we evaluate the effect of a novel class of PKC ligands, the diacylglycerol (DAG)-lactones, as inducers of apoptosis in LNCaP cells. These unique ligands were designed using novel pharmacophore- and receptor-guided approaches to achieve highly potent DAG surrogates. Two of these compounds, HK434 and HK654, induced apoptosis in LNCaP cells with much higher potency than oleoyl-acetyl-glycerol or phorbol 12,13-dibutyrate. Moreover, different PKC isozymes were found to mediate the apoptotic effect of phorbol 12-myristate 13-acetate (PMA) and HK654 in LNCaP cells. Using PKC inhibitors and dominant negative PKC isoforms, we found that both PKCalpha and PKCdelta mediated the apoptotic effect of PMA, whereas only PKCalpha was involved in the effect of the DAG-lactone. The PKCalpha selectivity of HK654 in LNCaP cells contrasts with similar potencies in vitro for binding and activation of PKCalpha and PKCdelta. Consistent with the differences in isoform dependence in intact cells, PMA and HK654 show marked differences in their abilities to translocate PKC isozymes. Both PMA and HK654 induce a marked redistribution of PKCalpha to the plasma membrane. On the other hand, unlike PMA, HK654 translocates PKCdelta predominantly to the nuclear membrane. Thus, DAG-lactones have a unique profile of activation of PKC isozymes for inducing apoptosis in LNCaP cells and represent the first example of a selective activator of a classical PKC in cellular models. An attractive hypothesis is that selective activation of PKC isozymes by pharmacological agents in cells can be achieved by differential intracellular targeting of each PKC.

The vanilloid receptor represents a promising target for drug development. Building on our previous strategies which have generated potent agonists for VR1, we now describe a series of novel N -(3-acyloxy-2-benzylpropyl)- N′ -dihydroxytetrahydrobenzazepine and tetrahydroisoquinoline thiourea analogues, several of which are potent VR1 antagonists. We report here the rationale for the design, the synthesis, and the in vitro characterization of activity in assays for [ 3 H]resiniferatoxin binding and 45 Ca influx using heterologously expressed rat VR1.

A series of alkyl tetrahydrofuran-2-carboxylates (1-4) bearing a new set of three pharmacophoric groups were tested as protein kinase C (PKC) ligands. The compounds were synthesized from commercially available glycidyl 4-methoxyphenyl ether. The correlation between their binding affinities for PKC-alpha and a conformational fit to phorbol ester indicates they mimic a pharmacophore model comprising the C20-OH, C3-C=O and C9-OH rather than that including the C13-C=O moiety.

The structure activity relationship on a series of ester and hydroxamate analogues of methionyl and isoleucyl adenylate has been investigated through introducing linkers between the 1'-position of ribose and adenine surrogates as methionyl-tRNA, and isoleucyl-tRNA synthetase inhibitors, respectively. The results indicate that ester analogue 23 was found to be a potent inhibitor of Escherichia coli methionyl-tRNA synthetase, and its interaction with the active site was proposed by a molecular modeling study.

A series of N -(3-acyloxy-2-benzylpropyl)- N ′-(4-hydroxy-3-methoxybenzyl)thiourea derivatives were investigated as vanilloid receptor ligands in an effort to discover a novel class of analgesics. The proposed pharmacophore model of resiniferatoxin, which includes the C 20 -homovanillic moiety, the C 3 -carbonyl and the orthoester phenyl ring as key pharmacophoric groups, was utilized as a guide for drug design. The compounds were synthesized after several steps from diethylmalonate and evaluated in vitro in a receptor binding assay and in a capsaicin-activated channel assay. Additional evaluation of analgesic activity, anti-inflammatory activity and pungency was conducted in animal models by the writhing test, the ear edema assay, and the eye-wiping test, respectively. Among the new compounds, 23 and 28 were found to be the most potent receptor agonists of the series with K i values of 19 nM and 11 nM, respectively. Their strong in vitro potencies were also reflected by an excellent analgesic profile in animal tests with ED 50 values of 0.5 μg/kg for 23 and 1.0 μg/kg for 28 . Relative to capsaicin these compounds appear to be ca. 600 and 300 times more potent. Both 23 and 28 were found to be less pungent than capsaicin based on the eye-wiping test. However, the compounds did not show significant anti-inflammatory activity. A molecular modeling study comparing the energy-minimized structures of resiniferatoxin and 35 demonstrated a good correlation in the spatial disposition of the corresponding key pharmacophores. The thioureas described in this investigation, which were designed as simplified resiniferatoxin surrogates, represent a novel class of potent vanilloid receptor agonists endowed with potent analgesic activity and reduced pungency.

We synthesized and evaluated 1-(4-fluorobenzyl)-4-[(5,6-dimethoxy-1-oxoindan-2-yl)methyl]piperidine (4-FDP), which is an analog of donepezil. The 4-[(18)F]FDP was prepared by reductive alkylation of debenzylated donepezil with 4-[(18)F]fluorobenzaldehyde in high radiochemical yield (decay-corrected, 40-52%) and with high effective specific activity (30-38 GBq/micromol). Tissue distribution studies in mice demonstrated nonspecific distribution of the 4-[(18)F]FDP in brain regions, suggesting that this radioligand may not be a suitable agent for in vivo studies of acetylcholinesterase (AChE), despite its potent in vitro biological activity.

The design of potent protein kinase C (PK-C) ligands with low nanomolar binding affinities was accomplished by the combined use of pharmacophore- and receptor-guided approaches based on the structure of the physiological enzyme activator, diacylglycerol (DAG). Earlier use of the former approach, which was based on the structural equivalence of DAG and phorbol ester pharmacophores, identified a fixed template for the construction of a semirigid "recognition domain" that contained the three principal pharmacophores of DAG constrained into a lactone ring (DAG-lactones). In the present work, the pharmacophore-guided approach was refined to a higher level based on the X-ray structure of the C1b domain of PK-Cdelta complexed with phorbol-13-O-acetate. A systematic search that involved modifying the DAG-lactone template with a combination of linear or branched acyl and alpha-alkylidene chains, which functioned as variable hydrophobic "affinity domains", helped identify compounds that optimized hydrophobic contacts with a group of conserved hydrophobic amino acids located on the top half of the C1 domain where the phorbol binds. The hydrophilic/hydrophobic balance of the molecules was estimated by the octanol/water partition coefficients (log P) calculated according to a fragment-based approach. The presence of branched alpha-alkylidene or acyl chains was of critical importance to reach low nanomolar binding affinities for PK-C. These branched chains appear to facilitate important van der Waals contacts with hydrophobic segments of the protein and help promote the activation of PK-C through critical membrane interactions. Molecular modeling of these DAG-lactones into an empty C1b domain using the program AutoDock 2.4 suggests the existence of competing binding modes (sn-1 and sn-2) depending on which carbonyl is directly involved in binding to the protein. Inhibition of epidermal growth factor (EGF) binding, an indirect PK-C mediated response, was realized with some DAG-lactones at a dose 10-fold higher than with the standard phorbol-12, 13-dibutyrate (PDBU). Through the National Cancer Institute (NCI) 60-cell line in vitro screen, DAG-lactone 31 was identified as a very selective and potent antitumor agent. The NCI's computerized, pattern-recognition program COMPARE, which analyzes the degree of similarity of mean-graph profiles produced by the screen, corroborated our principles of drug design by matching the profile of compound 31 with that of the non-tumor-promoting antitumor phorbol ester, prostratin. The structural simplicity and the degree of potency achieved with some of the DAG-lactones described here should dispel the myth that chemical complexity and pharmacological activity go hand in hand. Even as a racemate, DAG-lactone 31 showed low namomolar binding affinity for PK-C and displayed selective antitumor activity at equivalent nanomolar levels. Our present approach should facilitate the generation of multiple libraries of structurally similar DAG-lactones to help exploit molecular diversity for PK-C and other high-affinity receptors for DAG and the phorbol esters. The success of this work suggests that substantially simpler, high-affinity structures could be identified to function as surrogates of other complex natural products.

A series of 3-acyloxy-2-phenalkylpropyl amides and esters of homovanillic acid were designed and synthesized as vanilloid receptor agonists containing the three principal pharmacophores of resiniferatoxin. Amide analogues 23, 5 and 11 were found to be potent agonists in vanilloid receptor assay both for ligand binding and for activation.

In recent years, there have been considerable efforts to search for naturally occurring substances for intervention of carcinogenesis. Many components from medicinal or dietary plants have been identified to possess potential chemopreventive properties. For instance, curcumin, a yellow colouring agent from turmeric (Curcuma longa Linn., Zingiberaceae) has been shown to inhibit tumor formation in diverse animal models. Alpinia oxyphylla Miquel that also belongs to ginger family has been used in oriental herbal medicine. In the present work, we have evaluated the anti-tumor promoting potential of yakuchinone A (1-[4'-hydroxy-3'-methoxyphenyl]-7-phenyl-3-heptanone) and yakuchinone B (1-[4'-hydroxy-3'-methoxyphenyl]-7-phenylhept-1-en-3-one), major pungent ingredients of A. oxyphylla. Thus, topical application of yakuchinone A or B significantly suppressed TPA-induced epidermal ornithine decarboxylase activity. They also reduced TPA-stimulated production of tumor necrosis factor-alpha in cultured human promyelocytic leukemia (HL-60) cells. Both compounds blunted the TPA-induced superoxide generation in differentiated HL-60 cells in a concentration-related manner and also inhibited lipid peroxidation in rat brain homogenates. Furthermore, yakuchinone A and yakuchinone B nullified the activation of the activator protein-1 (AP-1) in immortalized mouse fibroblast cells in culture. These findings indicate that pungent diarylheptanoids from A. oxyphylla have anti-tumor promotional properties that can contribute to their chemopreventive potential.

A series of substituted tetrahydrofurans with an embedded glycerol backbone carrying additional tetrahydrofuranylideneacetate or tetrahydrofuranylacetate motifs were grouped into four distinct templates (I-IV) according to stereochemistry. The compounds were designed to mimic three essential pharmacophores (C(3)-C=O, C(20)-OH and C(13)-C=O) of the phorbol esters according to a new, revised model. The tetrahydrofuran ring was constructed from glycidyl 4-methoxyphenyl ether, and the structures of the isomeric templates were assigned by NMR spectroscopy, including NOE. The binding affinity for protein kinase C (PKC) was assessed in terms of the ability of the ligands to displace bound [(3)H-20]phorbol 12, 13-dibutyrate (PDBU) from a recombinant alpha isozyme of PKC. Geometric Z- and E-isomers (1 and 3, respectively) containing a tetrahydrofuranylideneacetate motif were the most potent ligands with identical K(i) values of 0.35 microM. Molecular modeling studies of the four templates showed that the rms values when fitted to a prototypical phorbol 12,13-diacetate ester correlated inversely with affinities in the following order: I approximately IIIIIIV. These compounds represent the first generation of rigid glycerol templates seeking to mimic the binding of the C(13)-C=O of the phorbol esters. The binding affinities of the most potent compounds are in the same range of the diacylglycerols (DAGs) despite the lack of a phorbol ester C(9)-OH pharmacophore surrogate. This finding confirms that mimicking the binding of the C(13)-C=O pharmacophore of phorbol is a useful strategy. However, since the C(9)-OH and C(13)-C=O in the phorbol esters appear to form an intramolecular hydrogen bond that functions as a combined pharmacophore, it is possible the lack of this combined motif in the target templates restricts the compounds from reaching higher binding affinities.

Three compounds, 5-(acetoxymethyl)-5-(hydroxymethyl)-3-tetradecyl-2,5-dihydro-2-furanone (3), 5-(acetoxymethyl)-5-(hydroxymethyl)-3,3-dihexyltetrahydro-2-furano ne (4) and 5-(acetoxymethyl)-5-(hydroxymethyl)-3,3-dioctyltetrahydro-2-furano ne (5), were designed and synthesized as surrogates of the ultrapotent DAG analogue, 5-(acetoxymethyl)-5-(hydroxymethyl) 3-[(Z)-tetradecylidene]tetrahydro-2-furanone (1), a compound that showed high affinity for PKC-alpha (Ki = 35 nM) in a competition binding assay with [3H-20]phorbol-12,13-dibutyrate (PDBU). In an attempt to overcome the problem of generating geometrical E- and Z-isomers, as encountered with 1, the double bond was moved to an endocyclic location as in 3, or an additional alkyl chain was appended to C3 to give the corresponding 3,3-dialkyl saturated lactones (4 and 5). The lactone was constructed from glycidyl-4-methoxyphenyl ether in 5 steps. The target compounds showed reduced binding affinities for PKC-alpha with Ki values of 192 nM (3), 4,829 nM (4), and 2,812 nM (5), respectively. These results indicate that constrained DAG analogues having a tetrahydro-2-furanone template are effectively discriminated by PKC-alpha in terms of the direction of the long alkyl chain connected to the 3-position.

Bis-gamma-lactones (1, 2) having a perhydrofuro[3,4-c]furan-1,4-dione skeleton were designed as conformationally constrained diacylglycerol analogues. They were synthesized from D-apiose in 11 steps, and evaluated as PKC-alpha ligands by measuring their ability to displace bound [3H]-PDBU from the enzyme. The compounds showed moderate binding affinities with Ki values of 13.89 (+/- 5.67) microM and 11.47 (+/- 0.89) microM, respectively. Their similar binding affinities indicate that these two bicyclic compounds were not effectively discriminated by PKC-alpha in terms of the direction of the side chain as other ligands built on similar bis-gamma-lactones.

The synthesis of two sets of rigid diacylglycerol (DAG) analogues with either the (S)-DAG or (R)-DAG enantiomer embedded into a bis-gamma-butyrolactone template was accomplished stereoselectively from di-O-isopropylidene-alpha-D-apiose. The key step in both syntheses was the assemblage of the bicyclic perhydrofuro[3,4-b]furan ring system via a radical exo-dig intramolecular cyclization. A lipophilic undecanyl alkyl chain attached at C-3 of the fully assembled perhydrofuro[3,4-b]furan-2,4-dione (bis-gamma-butyrolactone) template can adopt two orientations with the one directed away from the concave face of the bicyclic system favored by a 4 to 1 ratio in each case. Evaluation of the final target pairs of enantiomers as PK-C alpha ligands revealed that the template containing an embedded (R)-DAG structure was more effective. The difference in binding affinity was also modulated by the direction of the alkyl chain.

5,5-Bis(hydroxymethyl)tetrahydro-2-furanone and its isomer 4,4-bis(hydroxymethyl)tetrahydro-2-furanone were investigated as possible templates for the construction of conformationally constrained analogues of the biologically important second messenger, diacylglycerol (DAG). The former lactone contains embedded within its structure an exact glycerol moiety, while in the latter the ring oxygen has been transposed to the other side of the carbonyl group. All target compounds were synthesized as racemates from 1,3-dihydroxy-2-propanone. The 5,5-bis(hydroxymethyl)tetrahydro-2-furanone proved to be the better template for the construction of DAG surrogates that were demonstrated to have high binding affinities for the biological target, protein kinase C (PK-C). The simplest target compounds derived from this template (3e and 3f) have one of the hydroxyl moieties functionalized either as a myristate or as an oleate ester. The simplest target compound (9c) derived from the ineffective 4,4-bis-(hydroxymethyl)tetrahydro-2-furanone template was investigated only with a myristoyl acyl chain. Reducing the long acyl chain to an acetyl moiety and attaching a compensating lipophilic chain to the lactone ring as an alpha-alkylidene moiety produced compounds 10e and 10f (Z-isomers) and 11e and 11f (E-isomers), which were constructed on the more effective 5,5-bis(hydroxymethyl)tetrahydro-2-furanone template. Targets 14c (Z-isomer) and 15c (E-isomer) were derived, in turn, from 4,4-bis(hydroxymethyl)tetrahydro-2-furanone. The affinities of these ligands for PK-C were assessed in terms of their ability to displace bound [3H-20]phorbol 12,13-dibutyrate (PDBU) from the single isozyme PK-C alpha. The biological data support the hypothesis that the increase in binding affinity for PK-C shown by some of these constrained DAG mimetics appears to be entropic in nature. Two of the designed ligands (10e and 10f) showed the highest affinities (34 and 24 nM, respectively) reported so far for a DAG analogue. Assuming that the interaction between these racemic compounds and PK-C is stereospecific, the potency of the active enantiomer is anticipated to double.

A detailed examination of the mode of binding of phorbol esters to protein kinase C led to a model of the phorbol binding site in the enzyme. The efficacy with which various synthetic diacylglycerol analogs and ribonolactones are able to bind to this site was determined by means of semiempirical quantum mechanical calculations using PM3, and an estimate of the binding energy was made in each case. Sixteen synthetic analogs of 1,2-diacylglycerol and two natural products were studied, and their calculated energies of binding to this model were correlated with the measured Ki values. The binding energies calculated for this receptor model, together with solubility and entropy considerations, allow prediction through regressive fit of free energies of binding which correlate very well with the measured binding constants.

Starting with l- or d-tri-O-acetylglucal, the corresponding l- and d-isomers of 4-O-tetradecanoyl-2,3-dideoxyglucono-1,5-lactone (2a and 2b) were synthesized as rigid diacylglycerol (DAG) analogues. Consistent with results obtained previously with the equivalent l- and d-1,4-lactones (1a and 1b), the l-isomer (2a) was more potent in activating protein kinase C (PK-C) and inhibiting the binding of [3H]phorbol-12,13-dibutyrate to the enzyme's regulatory domain. In these experiments the difference in potency observed between the optical antipodes of the gluconolactones (2a and 2b) was greatly increased relative to the corresponding ribonolactones (1a and 1b). These results indicate that PK-C is more able to discriminate between optical antipodes, in favor of the l-isomer, as the lactone ring increases from five to six.

In the above article [Wang Y, Szabo T, Welter JD, Toth A, Tran R, Lee J, Kang SU, Suh YG, Blumberg PM, and Lee J (2002) Mol Pharmacol 62: 947–956], please note the following corrections. Some authors were inadvertently omitted from the article. The complete and correct list of authors and