Azagrevellins, Part I

Grevellin Analogs with Affinity to the N-Methyl-D-aspartate (GlycineSite) Receptor, a Novel Lead Structure✩

Hermann Poschenrieder, Georg Höfner, and Hans-Dietrich Stachel*

Institut für Pharmazie/Zentrum für Pharmaforschung der Universität München, Butenandtstr. 7, D-81377 München, Germany

Key Words: Spirooxiranes; ring enlargement; piperidine-2,3,5-triones; NMDA (glycine site) receptor affinity;[3H]MDL 105,519 displacement

Summary

Introduction

It is generally accepted that L-glutamate acts as the primaryexcitatory transmitter in the mammalian central nervous sys-tem and that over-stimulation of the system causes degenera-tion and death of neurons. The N-methyl-D-aspartatereceptor, a subtype of ionotropic glutamate receptors, plays amajor role in this excitotoxicity of glutamate [1]. It is also wellknown that glycine is an obligatory co-agonist for NMDAreceptor activation [2, 3]. Therefore the glycine site on NMDAreceptors represents an interesting target in the developmentof potential neuroprotective and other drugs.

A number of compounds from different classes have beenrecognized as functional antagonists at the glycine site, interalia 4-hydroxyquinoline-2(1H)ones 1 [4], aryl-substituted 5-arylidene tetramic acids 2 [5], and 5-arylidene pyrrolidine-2,3,4-triones or PTOs 3 [6] (Scheme 1). An account of aspectsof structure-activity relationships of several compounds ac-tive at the glycine site of the NMDA receptor and possibletherapeutic applications has been given by Dannhardt andKohl [7].

In a recent paper we reported on the synthesis of isomeric6-arylidene piperidinetriones of types 4 and 5 [8]. As het-eroanalogs of naturally occurring 6-arylidene pyranetriones

(known as grevellins), the latter were named azagrevellins forthe sake of brevity. Because of the structural similarity of theazagrevellin isomers 4 and the pharmacologically active qui-nolines 1 we have tested compound 4 for NMDA receptorglycine site binding but found no activity at all. However, toour surprise some azagrevellins 5 showed a remarkable re-ceptor affinity in this preliminary testing, thus establishinggeneral structure 5 as a new lead structure. For a more detailedstudy we have now prepared some differently substitutedazagrevellins.

Chemistry

Only a few azagrevellins 5 have been prepared so far,starting with 5-benzylidene pyrrolidine-2,3,4-trione 10a andcertain diazoalkanes. This synthesis apparently has only lim-ited value for the preparation of differently substituted deriva-tives of 5 because of the limited accessibility of the diazocomponents. On the other hand there appear to be fewerrestrictions on the part of the arylidene pyrrolidine-2,3,4-tri-ones 10. To follow up this idea, we needed novel triones 10.The requisite triones were prepared similarly to trione 10a [6]

which had previously been obtained by a reaction sequenceinvolving compounds 6a–9a [9–11] as intermediates(Scheme 2).

Arch. Pharm. Pharm. Med. Chem. © WILEY-VCH Verlag GmbH, D-69451 Weinheim, 2000 0365-6233/00/0707/0211 $17.50 +.50/0

A series of piperidine-2,3,5-triones (azagrevellins) has been pre-pared. A new synthesis has been introduced using the rearrange-ment of spiroepoxides in the presence of triethyloxoniumtetrafluoroborate. The binding affinity toward the N-methyl-D-aspartate (glycine site) receptor has been measured to provide abasis for more detailed structure-activity studies. Azagrevellin 18dshowed the highest binding potency.

Scheme 1 Scheme 2

Azagrevellins 211

Starting with the known 5-arylidene tetramic acids 6b–e [5]

and 6f [9], acid catalyzed condensation with acetone affordedthe alkylidene pyrrolidinediones 7b–f. Oxidation with alka-line hydrogen peroxide led to oxides 8b–f and their cleavageby boron trifluoride or mineral acids to the reductones 9b–f.Oxidation of these compounds to the triones 10b–f wasaccomplished by elemental iodine.

Analogously to the above-mentioned reaction of trione 10awith aryldiazomethanes [8], on addition of phenyldiazo-methane to a solution of one of the triones 10b–f the respec-tive azagrevellins 12b–f were formed by a ring enlargementreaction. With excessive phenyldiazomethane these com-pounds were derivatized in part into their enolethers 11b–fwhich were easily cleaved by trifluoroacetic acid. In a cog-nate manner, the interaction of trione 10d and 4-chloro-phenyldiazomethane afforded enolether 13d and azagrevellin14d. In the same way the azagrevellin 15d was formed fromtrione 10d and ethyl diazoacetate. All new azagrevellinsexhibited a brilliant red color when dissolved in concentratedsulfuric acid. The maximum absorption for the cinnam-ylidene compound 12f was found at 574 nm.

To overcome the limitations of the synthetic route on thepart of the diazalkanes, we have looked for other methodsleading to azagrevellins by ring enlargement. House re-ported [13] that ketones and diazomethane gave the corre-sponding epoxides beside the homologous ketones and thatthe formation of the oxides was suppressed in the presence ofboron trifluoride. It was concluded that this was due to Lewisacid catalyzed rearrangement of the initially formed epox-ides.

There are a few examples of spiroepoxides being turnedinto cyclic carbonyl compounds by Brønsted or Lewis ac-ids [12,14–18]. The isomerization proceeds via a 1,2-shift andensuing electrophilic ring opening. However, depending onthe substituents at the epoxide moiety, the epoxide decompo-sition in presence of acids can take other paths [14, 16, 19, 20].If a Lewis acid catalyzed ring enlargement were possible withspiroepoxides like 17 then we would have a new synthesis ofazagrevellins and/or their isomers of type 4 with a wide scopein our hands (Scheme 3).

Epoxide 17a was obtained as a mixture of epimers onoxidation of the bis-benzylidene tetramic acid 16a which isknown to exist as a mixture of E/Z-isomers with respect to the3-benzylidene group [10]. Treatment with boron trifluoride orsulfuric acid oxide turned 17a into reductone 9a and benzal-dehyde exclusively. However, we found out that epoxide 17aunderwent the ring enlargement we hoped for, if we replacedthe acid by an alkylating agent. Triethyloxonium tetrafluoro-borate (Meerwein’s reagent) successfully yielded the knownazagrevellin 12a [8] from epoxide 17a. The yield, however,was poor in comparison to the above-mentioned standardsynthesis. Therefore we cannot say with certainty that therearrangement proceeded in a rigorously stereoselective man-ner. So far no attempts have been made to improve the yield,for example by separation of the 17a isomers.

In analogy to 16a we have prepared the bis-arylidenetetramic acids 16b–d from 5-benzylidene tetramic acid 6aand the corresponding substituted benzaldehydes. The newcompounds were again isolated as a mixture of E/Z isomerswith respect to the 3-arylidene groups. Oxidation with hydro-gen peroxide provided epoxides 17b–d as mixtures of twoisomers each of which were converted into the known aza-grevellin 14a [8] or the new azagrevellins 18c, d respectively.

The epoxides 17a/b may be N-methylated forming theepoxides 19a/b which likewise underwent ring enlargementwith Meerwein’s reagent forming the corresponding azagrev-ellins 20a and 20b [8]. It is important to note that the yieldsin these cases were much higher than in the syntheses ofN-unsubstituted azagrevellins. Therefore the use of N-pro-tecting groups may prove useful in future syntheses.

Because of the identity of azagrevellin 20b obtained in thisway and in the standard synthesis [8] there is no doubt aboutthe Z configuration of the 6-benzylidene group. Isomerizationof the enolether (Z)-21a into a mixture of E/Z isomers in aratio of 1:6 was caused by trifluoroacetic acid on prolongedstanding at ambient temperature. Characteristically, the 1HNMR signal for the vinyl proton of the new isomer wasshifted to higher field and the signal of the N-methyl protonsto lower field.

Azagrevellins are enolic compounds with an acidity com-parable to carboxylic acids and are therefore easily and selec-tively O-methylated by diazomethane. As a new exampleenolether 21a was obtained in this way from azagrevellin 20a.Because of the poor solubility of the azagrevellin in water pKavalues were measured in aqueous dioxane 1:2 and found tobe around 6.05 for N-methylated azagrevellins like 20b andaround 5.70 for N-unsubstituted compounds like 14b.

Pharmacological Results and Discussion

Selected azagrevellins 11–15 and 18 have been evaluatedfor their potency to inhibit [3H]MDL 105,519 binding at theNMDA receptor associated glycine site in pig cortical brainmembranes. The results are summarized in Table 1.Scheme 3

212 Poschenrieder, Höfner, and Stachel

Arch. Pharm. Pharm. Med. Chem. 333, 211–216 (2000)

The second highest affinity at the NMDA receptor wasshown by the diphenylated azagrevellin 12a. Chlorinatedphenyl substituents in the side chain (12b–d) did not essen-tially alter the receptor affinity. It is noteworthy that changingthe configuration of the benzylidene side chain (14e) as wellas the replacement of the benzylidene by a cinnamylideneside chain (14f) reduced the binding by an order of ten. Aneven more drastic reduction was observed with the N-meth-ylated azagrevellins 20. However, comparison of the affini-ties of 20a and 20b shows the significance of the substituentin 3-position. The highest receptor affinity with a Ki value of0.86 µM exhibited the 3-phenoxyphenyl substituted azagrev-ellin 18d.

Structurally the azagrevellins do not fit well into the phar-macophore model proposed for NMDA receptor bindingcompounds [21]. In contrast to the highly active 3-aryl-4-hy-droxyquinoline-2H(1H)-ones [4] and 3-aryltetramic acids [5,21] in this case the lipophilic aryl moiety is placed in 4-posi-tion and the acidic group in 3-position. Furthermore therequirement of a 1-NH group is to be questioned in the lightof our findings. As a new and perhaps essential feature of thenovel lead structures the chelating properties of the azagrev-ellins should be mentioned.

With this information at hand we consider it worthwhile toprepare another set of differently substituted azagrevellins forfurther testing and to include N-alkylated compounds as wellas hydrogenated derivatives of azagrevellins into screening.

Experimental Section

General

All melting points were determined with a Dr. Tottoli melting pointapparatus (Büchi) and are uncorrected. Infrared spectra were measured aspotassium bromide plates using an IR Spectrometer FT-IR 1600 Series(Perkin Elmer). Ultraviolet spectra were determined in methanolic solutionon UV/VIS Spectrometer Lambda 20 (Perkin Elmer). 1H NMR spectra were

recorded using tetramethylsilane as internal standard on a JEOL GSX 400spectrometer (Jeol).

All new compounds gave correct elemental analyses which were carriedout applying an Analysator CHN-O-Rapid (Heraeus) or were done by I.Beetz, Mikroanalytisches Laboratorium, Kronach, Germany. The meltingpoints and spectroscopic data of the new compounds are listed in Table 2.

Chemistry

General Procedure for the Synthesis of Alkylidenepyrrolidinediones 7b–f

A solution of the appropriate tetramic acids 6b–e [5] or 6f [9] in acetone(100 ml) was refluxed in the presence of aqueous hydrochloric acid (35%, 5ml). Yellow crystals separated after a short period of time.

General Procedure for the Synthesis of Epoxides 8b–f and 17a–d

To a suspension of the appropriate bis-alkylidene pyrrolidinediones 7 or16 (10 mmol) and of hydrogen peroxide (30%; 2 ml) in methanol (30 ml)was added 2 N NaOH solution (1 ml). After 30 min the colorless precipitatewas isolated and washed with methanol. The oxides 17a–d are mixtures oftwo epimers.

General Procedure for the Synthesis of Reductones 9b–f

A solution of the appropriate epoxide 8 (4 mmol) in ice cold concentratedsulfuric acid (3 ml) was stirred for 15 min and then poured into ice water(100 ml). The precipitate was isolated and crystallized from formic acid.

General Procedure for the Synthesis of Pyrrolidinetriones 10b–f

To a stirred solution of the corresponding reductone 9 (2 mmol) in diox-ane/water 1:4 (10 ml) was added dropwise a 1 N iodine solution (20 ml). Thesolution was extracted twice with ethyl acetate and the combined organiclayers were dried with sodium sulfate. The volatile components were re-moved in vacuo and the residue was crystallized from dichloromethane.

General Procedure for the Synthesis of Pyridones 11b–f and 13d

A solution containing an excess of phenyldiazomethane [22] or 4-chlo-rophenyldiazomethane [22], respectively, in hexane (20 ml) was added to astirred solution of the corresponding pyrrolidinetrione 10 (2 mmol) in diox-ane (50 ml). After 1 h the solution was freed from the excess of diazoalkanesby addition of 1 ml of acetic acid. The volatile components were removed invacuo and the residue was crystallized from diisopropyl ether/ethanol 1:1.

Table 1. Affinity of new ligands (azagrevellins) at the NMDA (glycine site) receptor.

——————————————————————————————————————————————————Compd. X R1 R2 R3 R4 Ki values (µM)——————————————————————————————————————————————————12b H C6H4Cl(4) Ph OH H 1.69 ± 0.3612c H C6H4Cl(2) Ph OH H 4.21 ± 1.1312d H C6H3Cl2(2,4) Ph OH H 3.59 ± 0.4212e Ph Br Ph OH H 56.912f H PhCH=CH Ph OH H 23.3 ± 2814d H C6H3Cl2(2,4) C6H4Cl(4) OH H 9.44 ± 0.9515a H Ph CO2Et OH H 35 ± 4.715d H C6H3Cl2(2,4) CO2Et OH H 31.412a H Ph Ph OH H 1.61 ± 0.2414a H Ph C6H4Cl(4) OH H 9.62 ± 0.6418c H Ph C6H4Cl(2) OH H 4.09 ± 0.6318d H Ph C6H4(3-OPh) OH H 0.861 ± 0.03920a H Ph Ph OH Me 10020b H Ph C6H4Cl(4) OH Me 63.4 ± 19.3——————————————————————————————————————————————————

Azagrevellins 213

Arch. Pharm. Pharm. Med. Chem. 333, 211–216 (2000)

Table 2. Chemical and physical data.

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Compd Analysis Mp (°C) UV (methanol, nm): IR (KBr, cm–1): ν 1H NMR ([D6]DMSO): δ Mol. Mass Yield (%) λ max (log ε)

—————————————————————————————————————————————————————————————

7b C14H12ClNO2 220 2298 (4.365) 3197, 1723, 1697, 1635 10.92 (s, 1H), 7.68–7.39 (m, 4H), 6.33 (s, 1H), 261.71 80 2.54 (s, 3H), 2.50 (s, 3H)

7c C14H12ClNO2 206 271 (4.344) 3208, 1721, 1697, 1630 10.95 (s, 1H), 7.71–7.31 (m, 4H), 6.48 (s, 1H), 261.71 60 62.55 (s, 3H), 2.51 (s, 3H)

7d C14H11Cl2NO2 248 276 (4.375) 3193, 1728, 1703, 1646, 11.03 (s, 1H), 7.71–7.40 (m, 3H), 6.39 (s, 1H), 296.15 85 1624 2.54 (s, 3H), 2.50 (s, 3H)

7e C14H12BrNO2 221 259 (4.382) 3160, 1725, 1707, 1617 CDCl3: 8.00 (s, 1H), 7.47–7.36 (m, 5H), 2.63 306.17 80 (s, 3H), 2.50 (s, 3H)

7f C16H15NO2 200 (dec) 319(4.484) 3051, 1714, 1682, 1624

253.30 80

8b C14H12ClNO3 210 263 (4.108), 336 (4.209) 3416, 3230, 1755, 1720, 11.40 (s, 1H), 7.67 (d, 2H), 7.43 (d, 2H), 6.39 277.71 95 1640 (s, 1H), 1.60 (s, 3H), 1.48 (s, 3H)

8c C14H12ClNO3 190 246 (4.073), 330 (4.002) 3220, 1754, 1725, 1640 11.46 (s, 1H), 7.76–7.35 (m, 4H), 6.49 (s, 1H), 277.71 75 1.60 (s, 3H), 1.49 (s, 3H)

8d C14H11Cl2NO3 194 250 (4.119), 332 (4.104) 3219, 1758, 1725, 1651 11.50 (s, 1H), 7.75–7.47 (m, 3H), 6.41 (s, 1H), 312.15 70 1.60 (s, 3H), 1.49 (s, 3H)

8e C14H12BrNO3 180 (dec) 319 (3.884) 3200, 1754, 1727, 1644, CDCl3: 8.80 (s, 1H), 7.50 (m, 5H), 1.76 (s, 3H), 322.17 75 1627 1.56 (s, 3H)

8f C16H15NO3 188 (dec) 369 (4.417) 3050, 1747, 1711, 1625 11.50 (s, 1H), 7.54–7.01 (m, 6H), 6.99 (d, 1H,269.30 90 J = 16 Hz), 6.26 (d, 1H, J =13 Hz), 1.60

(s, 3H), 1.47 (s, 3H)

9b C11H8ClNO3 200 (dec) 227 (4.068), 322 (4.358) 3438, 3341, 1705, 1660 10.09 (s, 1H), 9.32 (s, 1H), 8.95 (s, 1H), 7.48 237.64 85 (d, 2H), 7.36 (d, 2H), 6.02 (s, 1H)

9c C11H8ClNO3 250 (dec) 311 (4.133) 3356, 1756, 1709, 1649 9.26 (s, 1H), 8.12 (s, 1H), 7.62–7.20 (m, 4H), 237.64 80 6.22 (s, 1H)

9d / 9e Not isolated

9f C13H11NO3 180 (dec) 348 (4.471), 364 (4.409) 3221, 1702, 1681, 1604

229.23 75

10b C11H6ClNO3 149 265 (4.063), 331 (4.073) 3300, 1764, 1743, 1641, 11.18 (s, 1H), 7.66 (d, 2H), 7.48 (d, 2H), 6.39 235.63 85 1586 (s, 1H)

10c C11H6ClNO3 140 264 (4.044), 325 (3.839) 3320, 1764, 1724, 1646 11.21 (s, 1H), 7.69–7.37 (m, 4H), 6.50 (s, 1H)235.63 75

10d C11H5Cl2NO3 158 (dec.) 273 (4.111) 3258, 1770, 1718, 1648 11.29 (s, 1H), 7.71–7.64 (m, 3H), 6.42 (s, 1H)270.07 60

10e C11H6BrNO3 134 (dec) 231 (4.141), 313 (3.831) 3272, 1765, 1747, 1710, 280.08 1629

10f C13H9NO3 227.22 279 (4.052), 363 (4.381) 3269, 1748, 1714, 1683, 11.30 (s, 1H), 7.54–7.38 (m, 6H), 6.97 (d, 1H, 160 (dec) 60 1616 J = 16 Hz), 6.28 (d, 1H, J = 13 Hz)

11b C25H18ClNO3 133 337 (4.065) 3430, 1676, 1660, 1581 10.72 (s, 1H), 7.64–7.20 (m, 14H), 6.85 (s, 1H), 415.87 20 15.33 (s, 2H).

11c C25H18ClNO3 110 310 (4.322) 3187, 3060, 1673, 1663, 10.72 (s, 1H), 7.90–7.22 (m, 14H), 6.91 (s, 1H), 415.87 20 1625 5.32 (s, 2H)

11d C25H17Cl2NO3 145 335 (4.035) 3380, 1687, 1666, 1590 10.81 (s, 1H), 7.70–7.16 (m, 13H), 6.82 450.32 40 (1s, 1H), 5.32 (s, 2H)

11e C25H18BrNO3 189 327 (4.035) 3216, 1681, 1669, 1568 CDCl3: 8.32 (s, 1H), 7.41–6.99 (m, 15H), 460.33 50 5.30 (s, 2H)

11f C27H21NO3 184 383 (4.159), 434 (4.222); 3444, 1673, 1646, 1563407.47 40 concd. H2SO4: 574

—————————————————————————————————————————————————————————————–

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Arch. Pharm. Pharm. Med. Chem. 333, 211–216 (2000)

Table 2. Continued.

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Compd Analysis Mp (°C) UV (methanol, nm): IR (KBr, cm–1): ν 1H NMR ([D6]DMSO): δ Mol. Mass Yield (%) λ max (log ε)

—————————————————————————————————————————————————————————————

12a[8] C18H13NO3 216–217 242 (4.220), 340 (4.128) 3285, 1675, 1652, 1630 11.32 (s, 1H), 10.68 (s, 1H), 7.60–7.33 (m, 10H),291.31 12 6.95 (s, 1H)

12b C18H12ClNO3 205 (dec.) 248 (4.163), 343 (4.214) 3268, 1674, 1653, 1633, 11.26 (s, 1H), 10.79 (s, 1H), 7.65–7.28 (m, 9H),325.75 65 1588 6.90 (s, 1H)

12c C18H12ClNO3 224 245 (4.209), 332 (4.192) 3272, 1662, 1639, 1596 10.79 (s, 1H), 7.53–7.34 (m, 4H), 6.96 (s, 1H)325.75 60

12d C18H11Cl2NO3 217 249 (4.265), 342 (4.213) 3247, 1685, 1653, 1592 11.39 (s, 1H), 10.88 (s, 1H), 7.71–7.23 (m,, 8H),360.15 90 6.86 (s, 1H)

12e C18H12BrNO3 118 323 (4.146) 3320, 1660, 1570370.20 50

12f C20H15NO3 195 382 (4.322) 3428, 1673, 1640, 1566317.34 60

13d C25H15Cl4NO3 178 337 (3.997) 3380, 1687, 1668, 1591 10.87 (s, 1H), 7.43–7.22 (m, 11H), 6.83 (s, 1H), 519.21 50 5.35 (s, 2H)

14a[8] C18H12ClNO3 233–235 250 (4.209), 351 (4.100) 3314, 1671, 1651, 1618 10.71 (s, 1H), 7.55–7.28 (m, 9H), 6.95 (s, 1H)325.75 14

14d C18H10Cl3NO3 236 252 (4.236), 339 (4.137) 3298, 3250, 1663, 1594 10.93 (s, 1H), 7.70–7.37 (m, 8H), 6.87 (s, 1H)394.64 65

15d C15H11Cl2NO5 228 327 (4.108), 407 (3.905) 3252, 1703, 1625, 1565 10.84 (s, 1H), 7.69–7.47 (m, 3H), 6.80 356.156 15 (s, 1H), 4.24 (q, 2H), 1.25 (t, 3H)

16b C18H12ClNO2 221 340 (4.603) 3190, 1724, 1703, 1636, 11.22 (s, 0.6H), 11.19 (s, 0.4H), 8.61–7.39 309.75 75 1613 (m, 10H), 6.47 (s, 0.4H), 6.46 (s, 0.6H)

16c C18H12ClNO2 215 327 (4.551) 3161, 1724, 1641, 1697 11.31 (s, 0.6H), 11.28 (s, 0.4H), 8.74–7.40 309.75 80 (m, 10H), 6.49 (s, 0.4H), 6.44 (s, 0.6H)

16d C24H17NO3 216 328 (4.536) 3196, 1723, 1702, 1637, 11.20 (s, 1H), 8.52–7.07 (m, 15H), 6.46 367.40 90 1613 (s, 0.4H), 6.43 (s, 0.6H)

17a C18H13NO3 291.31 269 (4.242), 336 (4.153) 3201, 1728, 1642 11.43 (s, 1H), 7.61–7.36 (m, 10H), 6.47 (s, 0.4H), 185 70 6.26 (s, 0.6H), 4.78 (s, 0.4H), 4.61 (s, 0.4H)

17b C18H12ClNO3 208 232 (4.189), 271 (4.290), 3226, 1754, 1728, 1639 11.40 (s, 1H), 7.64–7.39 (m, 9H), 6.47 (s, 0.4H), 325.75 75 337 (4.140) 6.27 (s, 0.6H), 4.80 (s, 0.4H), 4.63 (s, 0.4H)

17c C18H12ClNO3 176 272 (4.181), 333 (4.159) 3232, 1759, 1729, 1640 7.67–7.39 (m, 9H), 6.50 (s, 0.4H), 6.26 325.75 90 (s, 0.6H), 4.79 (s, 0.4H), 4.68 (s, 0.4H)

17d C24H17NO4 180 270 (4.268), 336 (4.145) 3224, 1729, 1642, 1585 11.51 (s, 0.6H), 11.25 (s, 0.4H), 7.66–6.93 383.40 65 (m, 14H), 6.52 (s, 0.4H), 6.31 (s, 0.6H),

4.81 (s, 0.4H), 4.63 (s, 0.4H)

18c C18H12ClNO3 200(dec.) 327 (3.871) 3265, 1658, 1640, 1588 7.59–7.36 (m, 9H), 6.91 (s, 1H)325.75 15

18d C24H17NO4 196 349 (4.194) 3258, 1655, 1634, 1587 10.66 (s, 1H), 7.57–6.93 (m, 15H)383.40 10

19a C19H15NO3 Oil 262 (4.196), 320 (3.794) 2970, 1755, 1735, 1642 CDCl3:7.63–7.34 (m, 10H), 6.92 (s, 0.4H), 305.33 65 6.73 (s, 0.6H), 4.78 (s, 0.4H), 4.62 (s, 0.4H)

19b C19H14ClNO3 –339.78 50

minor isomer 160 263 (4.362), 325 (3.859) 2923, 1759, 1730, 1646 CDCl3: 7.59–7.26 (m, 9H), 6.94 (s, 1H), 4.59 (Rf 0.66) 20 (s, 1H), 2.94 (s, 3H)

major isomer 112 227 (4.177), 264 (4.222), 2923, 1760, 1736, 1637 7.57–7.23 (m, 9H), 6.75 (s, 1H), 4.75 (s, 1H), (Rf 0.33) 30 315 (3.876) 3.05 (s, 3H)

20a C19H15NO3 193 242 (4.292), 329 (4.204) 3273, 1658, 1636, 1589 7.43–7.30 (m, 10H), 7.13 (s, 1H), 2.97 (s, 3H);305.33 35 CDCl3: 7.95 (s, 1H), 7.45–7.24 (m, 10H),

7.16 (s, 1H), 3.04 (s, 3H)

20b [8] C19H14ClNO3 184 245 (4.225), 330 (4.110) 3296, 1656, 1636, 1580 8.03 (s, 1H), 7.47–7. 39 (m, 9H), 7.13 (s, 1H), 339.78 30 2.96 (s, 3H)

21a C20H17NO3 112 325 (3.992) 2946, 1668, 1615, 1590 8.30 (s, 1H), 7.46–7.29 (m, 9H), 7.03 (s, 1H), 319.36 70 3.93 (s, 3H), 2.94 (s, 3H); CDCl3: 7.39–7.25

(m, 10H), 7.19 (s, 1H), 3.85 (s, 3H), 3.03 (s, 3H)—————————————————————————————————————————————————————————————–

Azagrevellins 215

Arch. Pharm. Pharm. Med. Chem. 333, 211–216 (2000)

General Procedure for the Synthesis of Azagrevellins 12b–f and 14d

A solution of the corresponding pyridone 11 or 13d (1 mmol) in tri-fluoroacetic acid (3 ml) was left at room temp. for 15 min. Then the volatilecomponents were removed in vacuo and the residue was crystallized frommethanol.

General Procedure for the Synthesis of Bis-arylidenepyrrolidinediones 16b–d

A solution of 5-benzylidene tetramic acid 6a [9] (1.75 g, 10 mmol) ormethyl 5-benzylidene-4-hydroxy-3-pyrroline-4-carboxylate (9) (2.30 g,10 mmol) in acetic acid (50 ml) was heated with the corresponding aldehyde(15 mmoles) and aqueous hydrochloric acid (35%, 5 ml) for 1 h. The pre-cipitates appearing on cooling were isolated and crystallized from methanol.The products are mixtures of the E/Z isomers.

General Procedure for the Synthesis of Azagrevellins 12a, 14a, 18a, b and20a, b

A solution of the corresponding epoxides 17 or 18 (4 mmol) and triethyl-oxonium tetrafluoroborate (1.0 g, 6 mmol) in dichloromethane (30 ml) wasstirred at room temp. for 1 d. Then the solution was shaken repeatedly withwater until the aqueous phase was neutral. The organic layer was dried withsodium sulfate. The volatile components were removed in vacuo and theresidue was crystallized from diisopropyl ether/ethanol 1:1.

(Z)-Ethyl 6-(2,4-Dichlorobenzylidene)-2,5-dioxo-3-hydroxy-1,2,5,6-tetra-hydropyridine-4-carboxylate (15d)

A solution of compound 10d (0.27 g, 1 mmol) in dioxane (10 ml) washeated in a sealed tube with ethyl diazoacetate (0.55 g, 5 mmol) to 80 °C for1 h. The solvent was removed and the residue dissolved in trifluoroaceticacid (5 ml). After 30 min the solvent was evaporated and the residue crystal-lized from diisopropyl ether/ethanol 1:1.

(Z)-5-Benzylidene-2,4-dioxo-1-methyl-pyrrolidine-3,3′-spiro-2′-phenyl-oxirane (19a) [23]

To a stirred solution of compound 17a (0.87 g, 3 mmol) in dimethylform-amide (40 ml) was added of sodium hydride (0.16 g, 4 mmol; as a 60%suspension in mineral oil). After 30 min at ambient temperature, methyliodide (0.56 g, 4 mmol) was added and the mixture was again stirred for 1 h.The reaction mixture was diluted with water (100 ml) and twice extractedwith dichloromethane. The combined organic layers were dried with sodiumsulfate. After removal of the solvent the residue was crystallized fromdiisopropyl ether/ethanol 1:1 yielding a 3:2 mixture of the epimers.

(Z)-5-Benzylidene-2,4-dioxo-1-methyl-pyrrolidine-3,3′-spiro-2′-(4-chlorophenyl)-oxirane (19b)

This compound was prepared analogously to 19a from compound 17b(0.97 g, 3 mmol). Crystallization from diisopropyl ether/ethanol 1:1 fur-nished a 3:2 mixture of the epimers in 55% yield. The isomers were separatedby column chromatography eluting with diethyl ether/petrol ether 1:1. Majorisomer: Rf 0.33, minor isomer: Rf 0.66.

(Z)-6-Benzylidene-3-methoxy-4-phenyl-1-methyl-1,2,5,6-tetrahydro-pyridine-2,5-dione (21a)

Compound 20a (0.61 g, 2 mmol) was treated with an excess of an etherealsolution of diazomethane. After the evolution of nitrogen had ceased thesolution was evaporated to dryness and the residue crystallized from diiso-propyl ether/ethanol. Leaving a solution of 21a in trifluoroacetic acid for 2 dat room temp. led to a mixture of the Z and the not isolated E isomer at a ratioof 6:1; 1H NMR ([D6]DMSO): δ = 7.44–7.27 (m, 10H), 6.98 (s, 1H), 3.83(s, 3H), 3.41 (s, 3H).

Pharmacology

[3H] MDL 105,519 binding to pig cortical membranes was performed aspreviously described [24]. Test compounds insoluble in water were dissolvedby addition of DMSO. The total amount of DMSO in the assay did not exceed1% and inhibited binding only negligibly.

Ki values for test compounds were calculated from experiments with atleast six concentrations of test compounds using InPlot 4.0 (GraphPadSoftware, San Diego, CA). The KD value for [3H] MDL 105,519 used in theCheng-Prusoff equation [25] to calculate Ki values was determined in satura-tion experiments as 3.73 ± 0.43 nM for [3H] MDL 105,519. If not statedotherwise, data are expressed as means ± SEM of three experiments, eachcarried out in triplicate.

References

✩ Dedicated to Professor Fritz Eiden on the occasion of his 75th birthday.

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Received: February 29, 2000 [FP462]

216 Poschenrieder, Höfner, and Stachel

Arch. Pharm. Pharm. Med. Chem. 333, 211–216 (2000)