Structure and synthesis of some complex pyranoisoflavonoids from the bark ofDalbergia nitidulaWelw.exBak.

摘要

1978 137 Structure and Synthesis of Some Complex Pyranoisoflavonoids from the Bark of Dalbergia nitidula Welw. ex Bak. By Fanie R. van Heerden, E. Vincent Brandt, and David G. Roux,' Department of Chemistry, University of the Orange Free State, Bloemfontein, 9300 Republic of South Africa Exhaustive examination of the flavonoid content of the bark of Dalbergia niridula revealed, amongst other substances a mixture of eight novel and complex (35) -isoflavans leiocin, leiocinol, nitidulin, nitidulan, heminitidulan and (6aS,11 as) -pterocarpans nitiducarpin, hemileiocarpin, nitiducol. These insoflavonoids all possess the equivalent of prenyl or geranyl side-chains, which, with one exception, are cyclized to stereochemically related 2H-pyran moeities during biogenesis.Structures determined by physical means were substantiated for the isoflavans by a single synthesis. THEpractice of dressing wounds with the bark of the distribution of the species which ranges from tropical slender tree or shrub DaZbergia nitiduZa Welw. ex Bak. Africa south to northern and eastern Transvaal and (Leguminosae) by our indigenous African population Natal,' is at present unknown. has prompted the present the 1 E. Palmer and N. Pittman, ' Trees of Southern Africa,' vole extent of such practice, or whether it parallels the wide 11, Balkema, Cape Town, 1972, p. 936. J.C.S. Perkin I Structural examination of bark metabolites revealed, protons and a 2,2-dimethyl-ZH-pyran moiety 8p9 to be in addition to a group of glycosides, a novel class of assigned to ring A, four arrangements of substituents are pyrano-isoflavonoids (isoflavans and pterocarpans) , and possible.However, the abnormal low-field resonance led to the synthesis of a derivative of one of the iso- flavans. This group of compounds is of therapeutic interest, considering the reputed pathological activity of isoflavans as phytoalexin~,~?~ ant it umour agents .* and of pterocarpans as Compounds derived from the bark of D.nitidula com-prise five new 2rsquo;-hydroxyisoflavans named leiocin (1a), nitidulin (2a), nitidulan (1b), heminitidulan (2b), and leiocinol (lc), as well as four pterocarpans, nitiducarpin a; R1 = OH, R2 z H,R3 = Me (3a), hemileiocarpin (4), nitiducol (5), and leiocarpin b; Rrsquo;= OH, R2 = H,R3 = (3b), of which only the last was previously recorded.c ; Rrsquo; = R2 = OH, R3 = Me Remarkably, with the exception of nitiducol (5), all d ; Rrsquo; = 02CMe. R2 = H,R3 = Me possess a 223-pyran moiety attached to ring A; two e ; Rrsquo; = OMe, R2 = H, R3 = Me pterocarpans, nitiducarpin (3a) and leiocarpin (3b), are f ; Rrsquo; = R2 = 02CMe, R3 = Me analogues of the isoflavans nitidulan (lb) and leiocin (la), respectively. The basic skeletal structure of the isoflavans may be recognized from lH n.m.r. data. All display the com- plex ABMXXrsquo; system typical of the five-proton hetero- cycle ring c.~,rsquo; The H-3 signal occurs as an undefined rnultiplet (T 6.1-6.7) resulting from its coupling with the 2-and 4-protons. The 2- and 4-methylene groups show coupling characteristic of isoflavans, H-2,, and H-2,, resonating as the AM portion (doublet of doublets, and lsquo; triplet rsquo; respectively) of an AMX system, and H-4,, a; Rrsquo; = R~ = OH and H-4,, as a doublet of an AArsquo;B system, except for b; Rrsquo; = OH, R2 = H the more complex ABX system in the case of hemi-c ; Rrsquo; = R2 = OMe nitidulan (2b).Accordingly the appearance of the 4-d ; Rrsquo; = R2 = OEt methylene group does not correlate with the suggested 02CMe steric hindrance offered by the 2lsquo;-substituent on ring B in these instances. The natural isoflavans isolated may be subdivided into R two groups based on their ring B substitution pattern, namely 2lsquo;,4rsquo;,5lsquo; (1) or 2rsquo;,3rsquo;,4rsquo; (2). Thus for leiocin (la), with hydroxy- and methylenedioxy-groups allocated to ring B (from mass and lH n.m.r.spectra 899) ,the observed para-coupled singlets (z3.40 and 3.60) could originate from this ring only, and leave no alternative but the indicated 2rsquo;,4rsquo;,5rsquo;-substitution pattern. This conclusion b; R = Meis confirmed by the anticipated paramagnetic shift of the two singlets due to H-6rsquo; and H-3rsquo; respectively (z3.30, AT -0.1; T 3.40, AT -0.2 p.p.m.), of the monoacetate (Id), With the remaining ortho-coupled benzenoid E. Wong in lsquo; The Flavonoids,rsquo; eds. J. B. Harborne, T. J. Mabry, and H. Mabry, Chapman and Hall, London, 1975, pp. 791-795. H. D. Van Etten, Phytochernistry, 1976, 15,655. R. Kojima, S. Fukushima, A. Neno, and Y. Saiki, Chem. and Pharm. Bull. (Japan), 1970, 18,2555. I,rdquo;rdquo;GO)R. Braz Filho and 0.R. Gottlieb, Phytoclzemistry, 1971, 10, 0 rsquo;0 2433. 13 K. Kurosawa, W. D. Ollis, 13. T. Redman, I. 0. Sutherland, 0. R. Gottlieb, and H. Magalhiies Alves, Chem. Comm., 1968, 1265. A. Pelter and P. I. Amenechi, J. Ckem. SOC.(C), 1969, 887. A. J. East, W. D. Ollis, and R. E. Wheeler, J. ClLem. Soc. (C), of one of the ortho-coupled doublets (T 3.13) suggests its 1969, 365. I. Fleming and D. H. Williams, lsquo; Spectroscopic Methods in allocation to a proton meta to both oxygen functions, and Organic Chemistry,rsquo; McGraw-Hill, New York, 1966, p. 127. in the 5-as opposed to the 7-position, which would also be in biogenetic contrast to all known isoflavans. This is substantiated by synthesis. Two other isoflavans, leiocinol (lc) and nitidulan (lb), were found to contain ring B systems identical with that in leiocin, differing only with regard to ring A.The first possesses a hydroxy-group in addition to the 2,2-dimethyl-2H-pyran ring, the proposed arrangement for these substituents asin (lc) beingtentative,pending future synthesis. In the second a single methyl group on the 2,2-dimethyl-2H-pyran ring is replaced by a 4-methyl- pent-3-enyl chain, clearly defined by lH n.m.r.1deg; and confirmed by H-~rdquo;(T 4.49)/H-4rdquo;(~ 3.33) as well as H-6rdquo;(T ca. 7.95)/H-7rdquo;(T cn. 4.90) spin-spin decoupling. The mass spectrum of nitidulan (lb) exhibits a fragment-ation very similar to that of leiocin (la) after initial loss of the pentenyl side-chain (M -83), and chemical shifts of H-5 (d, T 3.19) and H-6 (d, T 3.65, J5.6 8.0 Hz) are remarkably similar to those of leiocin (d, T 3.13, and d, T 3.60, 15.6 8.0 Hz).The latter suggests an identical 7,8-coupling of the 2-methyl-2- (4-methylpent-3-enyl) -2H-pyran system to ring A. This arrangement of ring A substituents is also applicable to the remaining isoflavans, nitidulin (2a) and heminitidulan (2b), although they differ with respect to rings B. The mass and IH n.m.r. spectra of nitidulin (2a) leave little doubt as to the placement of two hydroxy-groups and a methoxy-group on ring B, but pose a problem as regards their arrangement in spite of lH n.m.r. features (dd, T 3.40 and 3.62, J 8.0 Hz), indicating a vicinal arrangement of substituents adjacent to the point of attachment of ring B.Following methylation to give the dimethyl ether (2c) it was shown by benzene-induced methoxy-shift experiments l1 that only one methoxy-group (AT +O.lO, +O.lO, and +0.30 p.p.m.) was ortho to an aromatic proton. Subsequent repetition of the experiment on the diethyl ether (2d) afforded a similar result (AT +0.32 p.p.m.) for the methoxy-function, thus substantiating the proposed 4rsquo;-methoxy- substitution pattern (2a) for ring B. In the case of heminitidulan (2b), with a single hydroxy- and a methoxy-group allocated to the ring B, the ARX system displayed by the aromatic protons could only be derived from a 2rsquo;,4lsquo;-arrangement of substituents, with the abnormally low-field resonance of the ortho-coupled doublet (T 2.96) allocated to H-6rsquo;.Final assignment of the alternative 2rsquo;- or 4rsquo;-positions to the hydroxy-or methoxy-groups can only be solved by synthesis, although the 2rsquo;-hydroxy-4rsquo;-methoxy-arrangementis favoured in view of the coexistence of heminitidulan (2b) and its pterocarpan analogue, hemileiocarpin (4). Structural elucidation of the pterocarpans was simpli- fied by the coexistence and isolation of the known leio- carpin (3b), identical with the product isolated from APuZeia Zeioca~pa,~ which served as useful reference for spectrometric comparison. Thus, nitiducarpin (3a) lo G. Cardillo, L. Merlini, and R. Mondelli, Tetrahedron, 1968, 497. l1 J. H. Bowie, J. Ronayne, and D. H. Williams, .I. Chem.. SOC. (B),1966, 785. differed from leiocarpin solely with regard to the sub-stitution of the 2,2-dimethy1-2H-pyran system by 2- methyl-2-(4-methylpent-3-enyl)-2H-pyran,readily recog- nized from lH n.m.r.data.7 In a like manner, lH n.m.r. and mass spectra of hemileiocarpin (4) compared favourably with those of leiocarpin (3b), proving the former to be devoid of methylenedioxy-function, but possessing a methoxy-group. This methoxy-group could be assigned to ring D on grounds of its mass spectrum, since the 3rdquo;,4rdquo;-dihydro-2lsquo;-hydroxy-2rsquo;rsquo;H-pyrano-isoflavan (6) which results from hydrogenation of hemileiocarpin permits retro-Diels-Alder fragment-ation. Apart from the appearance of ortho-coupled doublets, readily attributed to H-1 and H-2, in the aromatic region of the lH n.m.r. spectrum, the residual ABX system includes a doublet to low-field (7 2.73, J 8.5 Hz).By assigning the latter to H-7, meta relative to each of the two oxygen functions, the methoxy-group may be placed at C-9. Nitiducol (5) represents the only metabolite isolated from L). nitidula bark not possessing the 2H-pyran system, but instead the uncyclicized geranyl side-chain. Its lH n.m.r. spectrum showed virtually no deviation from that of leiocarpin (3b) in the aromatic region, indicating the same substitution pattern, but with the conventional 2H-pyran system replaced by hydroxy and geranyl groups. The ortho-relationship of these was confirmed by the i.r. spectrum, which exhibited a hydroxy-group (3 000 cm-l) hydrogen-bonded l2 to the 2,3-vinyl function of the geranyl side-chain.Thus, all the physical data, including the mass spectrum,13 are in line with the proposed structure. Stereochemically the isoflavans were found to be identical all exhibiting a negative c.d. Cotton effect in the region 270-300 nm, indicative of a (3s)-configur-ation.6 Comparison of the 0.r.d. curves of 2rsquo;-O-methyl- leiocin (le) and (3s)-vestitol provided confirmation. Those isoflavans (lb), (2a) and (2b)l with an additional chiral centre at C-2rdquo; showed a second but positive c.d. Cotton effect (240-290 nm) implying the same con-figuration at C-2rdquo;. This could not be defined on account of lack of suitable reference compounds. The ptero- carpans (3a), (3b), (4), and (5) similarly feature Cotton effects corresponding to that of leiocarpin (3b) (positive 240-270 nm ; negative 270-320 nm), previously shown to have the (6aS,llaS)-configuration by com-parison with (6aR,1 laR)-pter~carpin.~ This was sub-stantiated for the new pterocarpans by their large posi- tive optical rotations, characteristic of (gas, 11aS)- pter0~arpans.l~ Nitiducarpin (3a), with an additional C-2rsquo; chiral centre furnished a subsidiary positive Cotton effect (260-290 nm) resembling that of analogous iso- flavans, and possibly indicating the same configuration at this point.From the above, the stereochemistry of iso- flavan and pterocarpan metabolities from D.nitidula is l2 A. W. Raker and A. T. Shulgin, J. Amer. Chem. SOC.,1959, 81, 4524. l3 E. Ritchie and W. C. Taylor, Tetrahedron Letters, 1964, 23, 1437.l4 I,. Verbit and J. W. Clark-Lewis, Tetrahedron, 1968.24, 5519. J.C.S. Perkin I Ac20 -C 5H5N1 1MeMgl H2,Pd-C1 iH2IPd- + oo AcO bsol; ' 2 NaOH-MeOH1 (la) SCHEME1: R = CH,OMe, R'= CH,OMe, R2= CH,Ph SCHEME2 : R=Me, R1=CH20Me, R2=CH,Ph identical at the corresponding position in their hetero- cycles. Noteworthy, therefore, is the natural co-existence of isoflavans and pterocarpans bearing strong structural and stereochemical resemblance to each other. This phenomenon is highly reminiscent of the findings of Dewick and Martin l5linking these two classes of com-pounds by a common biogenetic precursor, most likely an isoflavan-4-01.l~ In order to obtain confirmatory evidence of the struc- tures of the related isoflavans, an attempt was made to synthesise leiocin (la).Synthesis of conventional isoflavans entails reduction of the corresponding iso- flavone obtained from oxidative cyclization and re-arrangement of a chalcone with thallium trinitrate (TTN) 17. A similar route but providing for insertion of the 2,2-dimethyl-2H-pyran ring was envisaged for leiocin. This meant deferring insertion to the final step in order to avoid hydrogenation of the 3rdquo;,4rdquo;-double bond of the pyran ring during reduction of the flavonoid heterocycle. In addition this also required selective blocking of the 2rsquo;-hydroxy-group to prevent entry of the 2,2-dimethyl-2H-pyran moiety on both 7-and 2rsquo;-hydroxy-groups. Such a synthesis was attempted as outlined in Scheme 1.Little difficulty was experienced during synthesis of fragments (7) and (8) by conven-tional methods.18-21 These condense with ease to the 4lsquo;-benzyloxy-2,2rsquo;-di-0-methylmethoxy-4,5-methylene-dioxychalcone (9) characterized by lH n.m.r. and the expected a-cleavage during mass spectral fragmentation. Hydrolysis following oxidative rearrangement of this chalcone with TTN did not, however, proceed smoothly, producing several by-products and an unacceptably low yield (ca. 20) of the isoflavone. This was caused most likely by premature hydrolysis of the methoxymethyl groups of the intermediate a~eta1.l~ Successful applic- ation of this step in the synthesis called for stronger protection of the 2rsquo;-hydroxy-group.The synthetic route was accordingly modified to Scheme 2, employing the methyl ether of the aldehyde (8; R = Me), rather than the methoxymethyl ether (8; R = CH,OMe). This implied retention of the 2rsquo;- methoxy-group and unavoidably obtaining 2rsquo;-O-methyl- leiocin (l2a) as final product. Thus both chalcone formation (9; R = Me) and subsequent oxidation by into the isoflavan by the method described by Banda- ranayake et al.,22 the reagent, 3-hydroxy-1, l-dimethoxy- 3-methylbutane (14), being prepared by the action of a Grignard reagent (MeMgI) on acetoacetaldehyde dimethyl acetal (13). As expected, the pyridine-catalysed condensation of this reagent with the sub- strate (llb) yielded two products, identified by lH n.m.r.and mass spectra as 2rsquo;-O-methyl-leiocin (12a) and its structural isomer (12b). Synthetic 2rsquo;-O-methyl- leiocin was identical with the methyl ether of the natural compound (le), apart from the absence of optical activity. The natural isoflavans and pterocarpans will be examined for therapeutic properties. The glycosides from the bark of D. nitidula will be the subject of a future communication. EXPERIMENTAL Unless otherwise stated n.m.r. spectra (and Fourier transform analogues) were recorded for solutions in CDC1, (Me,Si as internal reference), U.V. spectra for solutions in MeOH, and i.r. spectra for solutions in CHC1,. Mass spectra were obtained with A.E.I. MS-9 and Varian CH-5 instruments. A J ASCO J-20 spectropolarimeter was employed for optical rotation and 0.r.d.determinations (solvent MeOH) . Systems used for separation of components comprised Whatman No. 3 paper (preparative paper chromatography), Merck silica gel 60 (column chromatography), and Merck silica gel 60 PF,,, (preparative t.1.c.). T.1.c. bands were located by U.V. illumination and/or spray reagents (HC10,- FeC1, or HCHO-H,SO,). Difficulties experienced throughout with the retention of organic solvents by the small quantities of oily or non-crystalline natural products available led to unsatisfactory C and H analyses in some instances. Here reliance was placed on accurate mass values, and purity was assessed by n.m.r. spectroscopy. Isolation of Constituents from D. nitidula Bark .-The bark (pulverised and dried; 718 g) was extracted with MeOH (6 x 1 1) at room temperature for 6 consecutive days and produced a brown solid (155 g) on evaporation of the combined extracts.Preparative paper chromatography (2 AcOH; upward migration) of a portion (30 g) of the extract yielded five crude fractions, only one of which (frac- tion E, 5.2 g; RF0.01) was investigated. Fraction E was TTN to 7-benzyloxy-4rsquo;,5rsquo;-methylenedioxy-2rsquo;-methoxy-rechromatographed (column chromatography ; cyclohexane-isoflavone (lob) proceeded without difficulty and in good yield, stressing the inhibitory role of the 2rsquo;-hydroxy- group in the oxidative rearrangement of the chalcone. Catalytic hydrogenation of the isoflavone produced the isoflavan analogue (1lb) in almost quantitative yield.As final step in the synthesis of 2rsquo;-O-methyl-leiocin (12a), a 2,2-dimethyl-2H-pyran ring was introduced l5 P. M. Dewick and M. Martin, J.C.S. Chem. Comm., 1976, 637. l6 P. M. Dewick, Phytochemistry, 1975, 14, 979; J.C.S. Chem. Comm., 1975, 656; P. J. van der Merwe, M.Sc. Thesis, University of the Orange Free State, Bloemfontein, January, 1977. l7 L. Farkas, A. Gottsegen, M. NbgrAdi, and S. Antus, J.C.S. Perkin I, 1974, 305. K. N. Campbell, P. F. Hopper, and B. K. Campbell, J. Org.Chem., 1951, 16, 1736. ethyl acetate, 3 : 1) into four subfractions (El-E,). T.1.c. separation (toluene-acetone, 199: 1, x 3) of fraction El (150 mg) yielded nitiducarpin (3a) (20 mg; RF 0.60),leiocarpin (3b) (32 mg; RF 0.55),and hemileiocarpin (4) (30 mg; RF 0.43).EIucidation of the composition of fraction E, (121 mg) proved more complicated and required an initial separation into two fractions (RF 0.31 and 0.25) by t.1.c. (n-hexane-acetone, 85 : 15, x 3). T.1.c. separation lo M. E. Oberholzer, G. J. H. Rall, D. Ferreira, and D. G. Roux, Tetrahedron Letters, 1976, 13, 1033. 2o K. C. Gulati, S. R. Seth, and K. Venkataraman, J. Chem. SOC.,1934, 1765. 21 A. I. Vogel, lsquo; A Textbook of Practical Organic Chemistry,rsquo; Longmans, London, 1967, p. 690. 22 W. M. Bandaranayake, L. Crombie, and D. A. Whiting, J. Chem. SOC. (C), 1971, 811. (chloroform-acetone, 99: 1, x 3) of the first of these produced nitiducol (5) (15 mg; Zip 0.80), nitidulan (lb) (17 mg; RF0.68), and heminitidulan (2b) (18 mg; R3-0.61); the second fraction yielded leiocin (la), (50 mg; Rp 0.58) upon purification by t.1.c.(chloroform-acetone, 99 : 1, x 3). Nitidulin (2a) (300 mg) was obtained from fraction E, by crystallization from cyclohexane. Fraction E, was similarly found to contain a single compound, leiocinol (lc) (45 mg; RF 0.25), following purification by t.1.c. (hexane-acetone, 65 : 35). Constituents from I). nitidula Bark and their Derivatives.- Leiocin (la) formed white needles (from EtOH), m.p. 150rdquo; (Found: C, 71.4; H, 5.8; Mrsquo;, 352.134. C,,H,,05 requires C, 71.6; H, 5.7; M, 352.131), nz/e 352(60, M+),337(100), 199(26), 188(32), 187(43), 186(13.2), 173(61), 164(43), 163(38), 151(37), 145(20), 137(2.3), and 135( 14.5) ; Amax.(log E) 292(4.11), 280(4.12), 227(4.55), and 207 nni (4.65); c.d. (c 0.048 4) el,,, 0, -2.28 x 105, el,,, 0, 1.20 x 104, el,,, 0, 0j230 3.00 x 105; 3.13(d, J 8.0 Hz, H-5), 3.28(d, J 10.0 Hz, H-4rdquo;), 3.40(~, H-6rsquo;), 3.60(d, J 8.0 Hz, H-6), 3.60(~, H-3rsquo;), 4.10 (s, OCH,O), 4.42(s, H-3rsquo;7, 5.08br (s, OH), 5.63(dd, J 10.0 and 4.0 Hz, H-2,,), 6.00(t, J 10.0 and 10.0 Hz, H-2,,), 6.33-6.63(m, H-3), 7.12(d, J 8.0 Hz, H-4), and 8.57(s, 2rdquo;-CH,). 2rsquo;-0-A cetyl-Zeiocin( Id), from acetylation of leiocin (20 mg) with acetic anhydride-pyridine was a white amorphous compound (21 mg), m.p. 114rdquo;; m/e 394(45y0, Mrsquo;) and 379(100); T 3.15(d, J 8.0 Hz, H-5), 3.30(~, H-6rsquo;), 3.32(d, J 10.0 Hz, H-4rdquo;), 3.40(~, H-37, 3.60(d, J 8.0 Hz, H-6), 4.00(s, OCH,O), 4.42(d, J 10.0 Hz, H-3rdquo;), 5.53-6.33(m, H-2,,, H-2,,, and H-3), 7.15(d, J 8.0 Hz, H-4), 7.70(s, COCH,), and 8.57(s, 2rdquo;-CH,).Zrsquo;-O-MethyZ-Zeiocin ( le), from methylation of leiocin (20 mg) with diazomethane was an oil (19 mg) (Found: C, 72.5; H, 6.9; M+, 366.147. C,,H,,O5 requires C, 72.1; H, 6.1; M, 366.147), m/e 366 (700/6, M+), 351(100), 199(21), 188(13.3), 187(9.7), 186(11.3), 185(29), 179(24), 178(76), 173(82), 166(40), 165(70), 163(20), 149(14.2), 145(21), 137(2.8), 135(40), and 133(65) ; 0.r.d. (c 0.0468) MI,,, oj MI,,, Jrsquo;~IxIcI-312j ojo, 78~ M129~ -703, Mlzss 0, MI283 312, M12s0 01 *I275 -156, LM1273 0, MI,,, 3 597; T 3.18(d, J 8.0 Hz,H-5), 3.35(d, J 10.0 Hz, H-ardquo;), 3.36(~, H-6rsquo;), 3.44(~, H-3rsquo;), 3.64(d, J 8.0 Hz, H-6), 4.10(~, OCH20), 4.45(d, J 10.0 Hz, H-3rdquo;), 5.68(dd, J 10.0 and 4.0 Hz H-2,,), 6.04(t, J 10.0 and 10.0 Hz, H-2,,), 6.22(s, 2rsquo;-OCH,), 6.30-6.60(m, H-3), 7.14(d, J 8.0 Hz, H-4), and 8.59(s, 2rdquo;-CH,).NitiduZin (2a) formed yellow cubes (from cyclohexane), m.p. 128rdquo; (Found: C, 73.8; H, 7.1; amp;If,422.209. C,,H,,05 requires C, 73.9; H, 7.2; M, 422.209), m/e 422(70, Mrsquo;), 407(31), 339(100), 199(9.8), 187(52), 186(3.0), 173(74), 166(11.3), 165(7.8), 153(49), 145(10.0), 139(8.2), and 137(8.2); A,,,. (log E) 283(4.01) and 295 nm (4.02); c.d. (C 0.044 0) 8,,, 0, O,,, -8.28 x 104, e,,,, 0, el,,, 1.10 x 106, el,,, 0, -4.14 x 105; T 3.20(d, J 8.0 Hz, H-5), 3.30(d, J 10.0 Hz, H-4rdquo;), 3.40(d, J 8.0 Hz, H-6rsquo;), 3.62(d, J 8.0 Hz, H-5rsquo;), 3.67(d, J 8.0 Hz, H-6), 4.52(d, J 10.0 Hz, H-3rdquo;), 4.33-5.10(m, H-7rdquo;, 2rsquo;-OH, and 3rsquo;-OH), 5.60(dd, J 10.0 and 4.0 Hz, H-2,,), 5.97(t, J 10.0 and 10.0 Hz, H-2,,), 6.20(s, 4rsquo;-OCH,), 6.20-6.67(m, H-3), 7.10(d, J 8.0 Hz, H-4), 7.50-8.1(m, H-6rsquo;7, 8.33- 8.50(m, H-5rdquo;), 8.33(s, 8rdquo;-CH,), 8.43 (s, 8rdquo;-CH,), and 8.63(s, 2rdquo;-CH,).2rsquo;,3lsquo;-Di-O-acetyZnztzduZin(2e) (21 mg) was obtained as a yellow oil by acetylation (acetic anhydride-pyridine) of J.C.S. Perkin I nitidulin (20 mg); m/e 506(7.3, Mf)and 423(100); T 7.70(s, 2 x COCH,). 2rsquo;- 3rsquo;-Di-O-methyZnitzduZin (2c), from methylation (diazo- methane) of nitidulin (30 mg) was a yellow oil (27 mg), rn/e 450(40, 111rsquo;) and 367(100); T 3.14(d, J 8.0 Hz, H-5), 3.20(d, J 10.0 Hz, H-4rdquo;), 3.30(d, J 8.0 Hz, H-6rsquo;), 3.34(d1 J 8.0 Hz, H-5rsquo;), 3.64(d, J 8.0 Hz, H-6), 4.50(d, J 10.0 Hz, H-3rsquo;7, 4.70-5.02 (m, H-7rdquo;), 5.33-6.00(m, H-2,, and H-Z,,), 6.10(s, 3 x OCH,), 6.30-6.70(m, H-3), 7.13(d, J 8.0 Hz, H-4), 7.70-8.10(m, H-6rdquo;), 8.20-8.50(m, H-5rsquo;7, 8.33(s, 8rdquo;-CH3), 8.40(s, 8rdquo;-CH3), and 8.62(s, 2rdquo;-CH,); z(C,D,) 2.97-3.73(m, H-5, H-6, H-5rsquo;, H-6rsquo;, and H-4rdquo;), 4.65(d, J 10.0 Hz, H-3rdquo;), 4.73-5.10(m, H-7rsquo;7, 5.50-5.83(m, H-2q), 6.07(t, J 10.0 and 10.0 Hz, H-2,,), 6.27(s, OCH,), 6.33(s, OCH,), 6.63(s, OCH,), 6.50-6.85(m, H-3), 7.23(d, J 8.0 Hz, H-4), 7.67-8.00(m, H-6rdquo;), 8.00-8.50(m, H-5rsquo;7, 8.33(s, 8rdquo;-CH3), 8.47(s, 8rdquo;-CH3), and 8.63(s, 2rdquo;-CH,).2rsquo;, 3rsquo;-Di-O-etlzyZnitiduZin (2d) was obtained by refluxing nitidulin (50 mg), anhydrous (120 ldquo;C) K,CO, (1 g), and EtI (1 g) in dry acetone (10 ml) for 2 h, filtration, and evaporation.The product was dissolved in ether (50 ml) and washed with water (2 x 30 ml). Evaporation of the ether produced the diethyl ether as a yellow oil (45 mg); m/e 478(30y0,M+)and 395(100) ; T 3.00-3.50(m, H-5, H-5rsquo;, H-6rsquo;, and H-4.7, 3.62(d, J 8.0 Hz, H-6), 4.45(d, J 10.0 Hz, H-3rdquo;), 4.70-5.00(m, H-7rdquo;), 5.50-6.10(m, H-2,,, H-2,,, and 2 x OCH,), 6.25(s, OCH,), 6.27-6.54 (m, H-3), 7.10(d, J 7.0 Hz, H-4), 7.50-8.10(m, H-6rsquo;7, 8.13-8.66(m, H-5rsquo;7, 8.33(s, 8rdquo;-CH3), 3.34(s, 8rdquo;-CH3), and 8.60(s, 3 x OCH,CH,) ; T(C,D,) 3.27-4.00(m, H-5, H-6, H-5rsquo;, H-6rsquo;, and H-4rdquo;), 4.90(d, J 10.0 Hz, H-3rdquo;), 5.00-5.30(m, H-7rdquo;), 5.67-6.67(m, H-2,,, H-2,,, and 2 x OCH,), 6.83(s, OCH,), 6.83-7.17(m, H-3), 7.47(d, J 8.0 Hz, H-4), 7.50-8.33(m, H-6rsquo;7, 8.33-8.58(m, H-5rdquo;), 8.62(s, 8rdquo;-CH,), 8.72(s, 8rdquo;-CH,), and 8.90(s, 3 x OCH,CH,). Nitzdulan (lb) was a white amorphous solid, m.p.55rdquo; (Found: C, 73.9; H, 6.7; Mf, 420.193. C26H2805 requires C, 74.3; H, 6.7; M, 420.194), m/e 420(13.7, M+), 405(5.2), 338(30), 337(100), 187(7.6), 174(3.1), 173(15.2), 169(5.5), 164(4.0), 151(6.1), and 135(2.0); A,,,. (log E) 290(4.13), 280(4.13), 227(4.53), and 205 nm (4.54); c.d. (C 0.050 0) 8350 0, cei,,, -1.38 x 105, 0, el,,,4.43 x lo5, 8,,, 1.10 x lo5; T 3.19(d, J 8.0 Hz, H-5), 3.33(d, J 10.0 Hz, H-4rsquo;7, 3.39(~, H-6rsquo;), 3.60(~, H-3rsquo;), 3.65(d,J 10.0 Hz, H-6), 4.12(~, OCHZO), 4.49(d, J 10.0 Hz, H-3rdquo;), 4.80---5.00(m, H-7rsquo;0, 5.66(dd, J 10.0 and 4.0 Hz, H-2,,), 6.00(t, J 10.0 and 10.0 Hz, H-2,,), 6.24-6.70(m, H-3), 7.12(d, J 8.0 Hz, H-4), 7.80-8.10(m1 H-6rdquo;), 8.20- 8.55(m, H-5rdquo;), 8.35(s, 8rdquo;-CH3), 8.42(s, 8rdquo;-CH3), and 8.62(s, 2rdquo;-CH,).Henzinitidulan (2b) was a white amorphous solid, m.p. 94rdquo; (Found: Mrsquo;, 406.212. C2,H3,O4 requires M, 406.214), m/e 406(18.0, Mrsquo;), 391(8.2), 337(11.5), 324(42), 323(100), 199(4.0), 187(20), 186(2.1), 173(7.3), 174(60), 150(9.5), 149(8.3), 137(22), 123(2.0), and 121(5.6); Amax. (log E) 280(4.14), 228(4.59), and 205nm (4.58); c.d. (c 0.047 2) el,,, 0, el,,, -7.10 x 104, p129g 0, PI,,,4.65 x 105, O,,, 0; T 2.97(d, J 8.0 Hz, H-67, 3.18(d, J 8.0 Hz, H-5), 3.31(d, J 10.0 Hz, H-4rsquo;7, 3.51(dd, J 8.0 and 2.0 Hz, H-5rsquo;), 3.63(d, J 2.0 Hz, H-3rsquo;), 3.64(d, J 10.0 Hz, H-6), 4.49(d, J 10.0 Hz, H-4rsquo;7, 4.80-5.00(m, H-7rsquo;7, 5.20br (s, OH), 5.62(dd, J 10.0 and 4.0 Hz, H-2,,), 5.96(t, J 10.0 and 10.0 Hz, H-2,,), 6.24(s, OCH,), 6.30-6.70(m, H-3), 7.00-7.18(m, H-4), 7.80-8.05(m, H-6rdquo;), 8.20-8.60(m, H-5rsquo;7, 8.34(s, 8rdquo;-CH,), 8.42(s, 8rdquo;-CH,), and 8.62(s, 2rdquo;-CH,).1978 Leiocinol (lc) was an amorphous solid, m.p. 70rdquo; (Found: Mf, 368.127. Calc. for C,,H,,O,: M, 368.126), m/e 368 (96, Mrsquo;), 353(88), 339(65), 218(23), 217(40), 215( 14.6), 206(62), 205(73), 204(46), 203(78), 202(15.1), 201(53), 19 1 (64), 190( 35), 189( 86), 187 (59), 1 7 7 (30), 176( 70), 175( 27), 173(45), 165(33), 164(100), 163(86), 162(29), 161(17.1), 153(29), 152(60), 151(84), 147(43), 137( l4.9), 135(40), 133(76), and 121(38); Amax. (log c) 297(3.85), 287(3.86), and 208 nm (4.41); c.d.(c 0.044 0) euro;I,,,-1.35 x lo3, p~,~,-6.21 x 103, el,,, 0, el,,, 6.48 x 103, el235 1.30 x lo4; T 3.35(d,J 10.0 Hz, H-4rsquo;7, 3.39, 3.47, and 3.60 (3 x s, H-6rsquo;, H-5, and H-30, 4.10(s, OCH,O), 4.43(d, J 10.0 Hz, H-3rsquo;7, 4.90br (s, 2 x OH), 5.50-6.30(m, H-2,, and H-2as), 6.30-6.76(m, H-3), 7.15(d, J 8.0 Hz, H-4), and 8.38(s, 2 x 2rdquo;-CH3). 2rsquo;,6-Di-O-acetyl-leiocinol(If) (21 mgj was obtained by acetylation of leiocinol (20 mg) with acetic anhydride- pyridine as an amorphous solid, m.p. 135rdquo;; m/e 452(87y0, M+); T 3.35(d, J 10.0 Hz, H-4rdquo;), 3.35 and 3.40(2 x s, H-5, H-3rsquo;, and H-67, 4.02(s, OCH,O), 4.42(d, J 10.0 Hz, H-3rsquo;7, 5.60--6.40(m, H-2 and H-3), 7.20(d, J 8.0 Hz, H-4), 7.70(s, 2 x COCH,), and 8.60(s, 2 x 2rdquo;-CH,).Leiocarpin (3b) afforded white needles (from EtOH), m.p. 96rdquo; (lit.,5 98rdquo;) (Found: M+, 350.133. Calc. for C21- H1805: M, 350.115), m/e 350(69, Mrsquo;) and 335(100); AmX. (log E) 305(4.06), 290(4.00), 227(4.78), and 205 nm (4.69); c.d. (c 0.048 0) 8,,, 0, el3,, -6.98 x lo5, 0, el,,, 1.10 x lo6; 0.r.d. (c 0.048 8) MI345 0, MI,,, -100 4, MI,,,* 0, MIz9, 1 721, MI,,,1434, MI,,, 1 721, MI,,, 6 166, MI,,, 0; ,IDz4 +215 (c 0.1300 in CHCl,); T 2.74(d, J 8.0 Hz, H-1), 3.27(~, H-7), 3.34(d, J 10.0 Hz, H-4rsquo;), 3.47(d, J 8.0 Hz, H-2), 3.55(~, H-lo), 4.08(~, OCHZO), 4.42(d, J 10.0 Hz, H-3rsquo;), 4.55(d, J 6.0 Hz, H-lla), 5.60- 5.90(m, H-6,,), 6.10-6.63(m, H-6,, and H-6a), and 8.58(s, 2 x 2rsquo;-CH,). Nitiducarpin (3a) was a white amorphous solid, m.p.84rdquo; (Found: M+, 418.177. C,,H,,O, requires M, 418.178), m/e 418(69, Mrsquo;), 403(6.1), 375(5.0), 350(6.4), 337(7.8), 338(30), 335(loo), 322(6.4), 321 (28), 198(2.7), 185( 27), 175( 6.2), 173( 25), 168( 7.4), 167( 36), 162( 3.8), 160( 6.0), 149(14.4), 113(7.4), 111(6.7), and lOg(5.7); A,,,. (log E) 307(3.81), 292(3.80), 230(4.38), and 205 nm (4.20); c.d. (c 0.452 0) el,,, 0, 6,1, -3.50 x 105, el,,, 0, OJ,,~7.22 x lo5; T(CD,),CO 2.73(d, J 8.0 Hz, H-11, 3.07(~, H-7), 3.32(d, J 10.0 Hz, H-4rsquo;), 3.52(d, J 8.0 Hz, H-2), 3.60(~, H-lo), 4.07(~, OCH,O), 4.34(d, J 10.0 Hz, H-3rsquo;), 4.49(d, J 6.0 Hz, H-lla), 4.60-5.03(m, H-7rsquo;), 5.47-5.80(m, H-64, 6.20-6.50(m, H-6,,, H-6a), 7.80-8.10(m, H-6rsquo;), 8.35(s, 8rsquo;-CH,), 8.40(s, 8rsquo;-CH3), 8.26-8.53(m, H-57, and 8.64(s, 2rsquo;-CH,) .Hernileiocarpin (4) was an oil (Found: M+, 336.138. Cz1Hz004 requires M,336.136), m/e 336(78, Mrsquo;), 335(7.9), 322(38), 321(100), 306(7.6), 293(7.4), 279(10.5), 213(1.6), 200( 1.4), 198( 2.0) , 185( 23), 173( 20), 167(27), 161( 12.7), 160(30), 153( 26), 150(9.3), 149(76), 148( 1.4), 139( 12.8), 113(14.1), and lll(7.7); A,,,. (log E) 287(2.97) and 245 nm (4.09); c.d. (c 0.047 6 in CHC1,) 8,,, 0, 8,,, -3.14 x lo5, 0, O,,, 6.40 x lo5; T(CD,),CO 2.73(2 x d, J 10.0 Hz, H-1 and H-7), 3.37(d, J 10.0 Hz, H-47, 3.52(d, J 8.0 Hz, H-2), 3.53(dd, J 8.0 and 2.0 Hz, H-8), 3.58(d, J 2.0 Hz, H-lo), 4.33(d, J 10.0 Hz, H-3rsquo;), 4.48(d, J 6.0Hz, H-lla), 5.50-6.00(m, H-6,,), 6.23(s, OCH,), 6.17-6.50(m, H-6,, and H-6a), 8.60(s, 2 x 2rsquo;-CH,).2rsquo;-Hydroxy-4rsquo;-methoxy-3rsquo;rsquo;,4rdquo;-dihydro-2rdquo;, 2rdquo;-dimethyl- pyrano6ldquo;,5ldquo; : 7,8isofEavanl5 (6). Hemileiocarpin (5 mg), dissolved in EtOH (4 ml) and acetic acid (1ml), was hydro- genated for 8 h at room temperature (3 atm) over 10 Pd-C. Subsequent filtration and evaporation yielded the isoflavan analogue (4 mg); m/e 340(39y0, Mrsquo;), 279(14.5), 216(28), 203(10.4), 192(17.2), 191(72), 190(2.5), 167(31), 161(14.3), 160(23), 151(12.2), 150(62), 149(100), 147(14.5), 137(41), 136(11.2), 135(37), 123(24), 121(20), 113(17.8), and 112( 10.5). NitiducoZ (5) was a white amorphous solid, m.p. 71rdquo; (Found: C, 73.7; H, 6.9; Mrsquo;, 420.193. C2,H2,05 requires C, 74.3 ; H, 6.7 ; M 420.194), rn/e 420( 96, Mrsquo;), 351(5.8), 335(9.4), 298(12.8), 297(38), 296(100), 295(16.5), 189(14.3), 175(11.5), 163(8.8), 162(16.8), 159(5.1), 151(10.0), 149(17.5), 147(11.7), 146(2.3), 135(25), 123(15.1), 121(7.4), 113(6.5), 111(11.1), and lOg(9.6); A,,,.(log z) 307(4.91), 283(3.64), and 207 nm (4.76); c.d. (c 0.043 6) 0, el,,, -3.49 x 105, el,,, 0, el,,, 1.05 x 106; villas. 3 ooo cm-l; T 2,74(d, J 8.0 Hz, H-l), 3.28(s, H-7), 3.43(d, J 8.0 Hz, H-2), 3.57(~, H-lo), 4.10(d, J 1.0 Hz, OCHZO), 4.51(d, J 6.0 Hz, H-lla), 4.60-5.98(m, H-2rsquo; amd H-67, 5.66-5.82(m, H-6,,), 6.26-6.68(m, H-6,,, H-6a, and H-lrsquo;), 7.96br(s, H-4rsquo; and H-57, 8.22(s, 3rsquo;-CH,), 8.34(s, 7rsquo;-CH,), and 8.42(s, 7rsquo;-CH,). Attempted Synthesis of Leiocin (la) .-4rsquo;-Benzyloxy-2rsquo;- hydroxyacetophenone was prepared from 2rsquo;,4rsquo;-dihydroxy- acetophenone (5 g) according to the method of Gulati et aZ.,,O the compound crystallizing from MeOH as platelets (3.08 g), m.p.104rdquo; (lit.,,, 110rdquo;); M+ 242; 7 -2.77(s, OH), 2.40(d, J 10.0 Hz, H-67, 2.64(s, PhCH,O), 3.52(dd, J 10.0 and 2.0 Hz, H-5rsquo;), 3.52(d, J 2.0Hz, H-37, 4.92(s, PhCH,O), and 7.47(s, COCH,). 4rsquo;-BenzyZoxy-2rsquo;-0-methoxymethylaceto~henone(7; R1 = CH,OMe, R3 = CH,Ph) . 4rsquo;-Renzyloxy-2rsquo;-hydroxyaceto-phenone (2.42 g), KOH (0.6 g), water (1.5 ml), and MeOH (10 ml) were heated to 96 ldquo;C for 2 11. The potassium salt obtained by evaporation was dried at 120 ldquo;C for 2 h and redissolved in a solution of 18-crown-6 (2.0 g) in dry acetonitrile (20 mg).ls The solution was stirred for 30 min at room temperature, MeOCH,Cl (1.2 ml) was slowly added, and a further 30 min was allowed for completion of the reaction.KC1 produced was filtered off and washed with ether, and the combined filtrates were evaporated. The product was dissolved in ether and washed with 10 (w/v) KOH (3 x 30 ml) followed by water (5 x 50 ml), producing the pure compound as a brown oil (1.87 g) on evaporation (Found: M+, 286.120. C,,H,O, requires M, 286.121); T 2.17(d,J 8.0 Hz, H-67, 2.62(~, PhCH,O), 3.20(d, J 2.0Hz, H-3rsquo;), 3.36(dd, J 2.0 and 8.0Hz, H-5rsquo;), 4.76(s, OCH,OCH,), 4.92(s, PhCH,O), 6.50(s, OCH,0CH3), and 7.40(s, COCH,). 2-Hydroxy-4,5-methylenedioxybenzaZdehyde. Dry HC1 gas was led through a mixture of 3,4-methylenedioxyphenol (5 g), HCN (7 ml solution), and Zn(CN), (5 g) in ether (100 ml; Na-dried) at 0 ldquo;C until the mixture was saturated (ca.5 h), after which it was kept at 0 ldquo;C euro;or 15 h.,, The ether was decanted and the iminium chloride hydrolysed with water (100 ml) at 96 ldquo;C for 30 min. During this process white crystals of the product were obtained. These were supplemented by steam-distillation of the filtrate, and the product was recrystallized from EtOH to give white needles (5.9 g), m.p. 125rdquo; (1it.,l8 125-126rdquo;); M+ 166; T(CD,),CO -1.87(~, OH), 0.17(~, CHO), 2.87(~, H-6), 3.50(s, H-3), and 3.88(s, OCH,O). 2-O-Methoxy-methyl-4,5-methylenedioxybenzaldehyde (8; R = CH,OMe) . 2-Hydroxy-4,5-methylenedioxybenzalde-hyde was methoxymethylated asdescribed. lo Crystallization from EtOH yielded white needles (2.4 g), n1.p.79" (Found: C, 57.2; H, 4.8. CloH,,05 requires C, 57.1; H, 4.8); M-' 210; T -0.33(s, CHO), 2.73(s, H-6), 3.20(s, H-3), 3.96(s, OCH,O), 4.75(s, OCH,OCH,), and 6.45(s, OCH20CH,). 4'-Benzyloxy- 2,2'- bis-O-methoxymethyl-4, B-methylene- dioxychalcone (9; R = R1 = CH20Me, R2 = CH2Ph). A solution of the acetophenone (7; R2 = CH2Ph, R1= CH2-OMe) (1.24 g) in EtOH (30 ml) and 60 (w/v) KOH (10 ml) was stirred for 30 min at room temperature, and the aldehyde (8; K = CH,OMe) (1.14 g) was added. When all the aldehyde had been consumed (t.l.c.), water (30 ml) was added, and the mixture acidified (~N-HC~) and extracted with ether (3 x 50 ml). The extract was washed with water (4 x 50 nil) and taken to dryness. T.1.c. (benzene- hexane-ethyl acetate, 5 : 4 : 2) produced the chalcone (RF 0.32) as a yellow oil (1.0 g), which crystallized from EtOH as yellow needles, m.p.90" (Found: C, 69.4; H, 5.5. C27-H,,O, requires C, 69.6; H, 5.4y0), m/e 478(4.2, M+); T 1.92(d, J 16.0 Hz, H-P), 2.28(d, J 8.0 Hz, H-6'), 2.60(~, PhCH,O), 2.70(d, J 16.0 Hz, H-a), 2.92(~, H-6), 3.16(d, J 2.0 Hz, H-3'), 3.23(d, H-3), 3.32(dd, J 8.0 and 2.0 Hz, H-5') , 4.07(~, OCHZO), 4.77(~, OCH,OCHJ, 4.85(~,OCH2-OCH,), 4.90(s, OCH2Ph), and 6.51(s, 2 x OCH,). 7-Benzyloxy- 2'-hydroxy-4', 5'-methylenedioxyisojfavone (10a; R2 = CH,Ph). TI(NO,), (385 mg), the chalcone (9; R = R1= CH,OMe, R2 = CH,Ph); (430 mg) and MeOH (100 ml) were stirred for 30 min, ~N-HC~ (10 ml) was added, and the mixture was refluxed for 5 h.17 After removal of the TINO, precipitate, the filtrate was extracted with CHCl, (3 x 50 ml) and the extract washed with 10 (w/v) NaHCO, (2 x 30 ml) followed by water (2 x 30 ml).Evaporation yielded the isoflavone as a white solid (70 mg), which was purified by t.1.c. (benzene-hexane-ethyl acetate, 5 : 4 : 2; Rp 0.42); m/e 388(19.2y0,M+),269(11.0), 227(6.2), 226(1.0), 162(5.3), 119(5.3), 92(10.2), 91(100) (owing to exceptionally low solubility of the pure isoflavone in a variety of solvents, full characterization was performed on the acetate). Acetylation (acetic anhydride-pyridine) of the isoflavone (50 mg) yielded the acetate (45 mg), crystallising from EtOH as white needles, m.p. 165" (Found: C, 69.7; H, 4.3; M+, 430.105.C25H1807 requires C, 69.8; H, 4.2; M, 430.105); T 1.76(d, J 9.0 Hz, H-5), 2.17(~, H-2), 2.53(~, OCH,Ph), 2.90(dd, J 9.0 and 2.0 Hz, H-6), 3.05(dJ J 2.0 Hz, H-8), 3.18(~, H-3'), 3.27(~, H-6), 3.07(~, OCH,O), 4.80(s, OCH,Ph), and 7.90(s, COCH,). Synthesis of 2'-O-Methyl-leiocin (12a) .-Methoxy-4,5- methylenedioxybenzaldehyde (8; R = Me). Methylation of 2-hydroxy-4,5-methylenedioxybenzalclehyde (2.5 g) with dimethyl sulphate, and crystallisation from EtOH produced white needles (1.65 g), m.p. 114" (lit.,l* 112"); M+ 180; T -0.32(~, CHO), 2.73(~, H-6), 3.42(~, H-3), 3.97(~, OCHZO), and 6.12(s, OCH,). 4'-Benzyloxy-2-methoxy-2'-O-methoxymethyl-4,5-methylene-dioxychalcone (9; R = Me, R1 = CH,OMe, R2 = CH,Ph). The acetophenone (7; R1= CH20Me, R2 = CH,Ph) (1.5 g) and the benzaldehyde (8; R = Me) (1.44 g) were condensed as described 23 to yield the chalcone, which was purified by t.1.c.(hexane-ethyl acetate, 3 : 1; RF 0.15) and crystallized from EtOH as yellow needZes (1.15 g), m.p. 125" (Found: C, 69.5; H, 5.3. C,5Hamp; requires C, 69.6; H, 5.4), m/e 448(40, M+); T 1.95(d, J 16.0 Hz, H-p), 2.30(d,J 9.0 Hz, H-67, 2.57(~, OCHZPh), 2.70(d, J 16.0 Hz, H-a), 2.92(~, H-6), 3.15(d, J 2.0 Hz, H-3'), 3.30(~, H-3), J.C.S. Perkin I 3.47(dd, J 2.0 and 9.0 Hz, H-5'), 4.03(s, OCH20), 4.77(s, OCH,OCH,), 4.88(s, OCH,Ph), 6.20(s, OCH,), and 6.50(s, OCH,OCH,) . 7-Benzyloxy- 2-nzethoxy-4', 5'-nzethylenedioxyisojZavone (lob; R2 = CH,Ph). Oxidation of the chalcone (9; R = Me, R1 = CH,OMe, R2 = CH,Ph) (0.9 g) by Tl(NO,), l7 produced the isoflavone, which readily crystallized from EtOH as yellow cubes (0.719 g), m.p.150" (Found: C, 71.4; H, 4.6. C2,H1,0, requires C, 71.6; H, 4.5); m/e 402(50y0, M'); T 1.78(d,J 9.0 Hz, H-5), 2.12(~, H-2), 2.56(~, OCH,- Ph), 2.95(dd, J 9.0 and 2.0 Hz, H-6), 3.07(d, J 2.0 Hz, H-8), 3.17(~, H-6'), 3.37(~, H-3'), 4.05(~, OCHZO), 4.83(~, OCH,Ph), and 6.30(s, OCH,). ( -I-)-7-Hydroxy-2'-methoxy-4',5'-methylenedioxyisojZavan (llb). The isoflavone (lob; R2 = CH,Ph) (250 mg) in EtOH (45 m1) and acetic acid (5 ml) was hydrogenated (room temperature, 3 atm, 6 h) over 10 Pd-C (250 mg).' After filtration, water (10 ml) was added, the EtOH evaporated off, and the residue extracted with CHC1, (3 x 50 ml).The extract was washed consecutively with 10 (w/v) NaHCO, (2 x 30 ml) and water (2 x 50 ml), yielding the isoflavan on evaporation. Crystallization from EtOH yielded white needles (170 mg), m.p. 168" (Found: C, 67.7; H, 5.5. C,,H1,O, requires C, 68.0; H, 5.4y0), m/e 300(55, M') ; .r(CD,),CO 193(s, OH), 3.08(d, J 8.0 Hz, H-5), 3.25(s, H-6'), 3.30(s, H-37, 3.62(dd, J 8.0 and 2.0 Hz, H-6), 3.68(d, J 2.0 Hz, H-8), 4.07(~, OCHZO), 5.78(dd, J 10.0 and 4.0 Hz, H-2q), 6.03(t, J 10.0 and 10.0 Hz, H-2,,), 6.18(s, OMe), 6.33-6.73(m, H-3), and 7.15(d, J 8.0 Hz, H-4). 3-Hydroxy-3-methyl- 1, l-diunethoxybutane ( 14).22 This was prepared from acetoacetaldehyde dimethyl acetal ( 13) (13.2 g) by the method of Randaranyake et ~l.,~, aas liquid, b.p. 74-78" at 80 mmHg (lit.,22 70-80" at 14 mmHg); T 5.33(t, J 6.0 Hz, H-l), 6.53(s, OH), 6.63(s, 2 x OCH,), 8.20(d, J 6.0 Hz, H-2), and 8.75(s, 2 x CH,). ( j-)-Z'-O-methyZ-Zeiocin (1).To a vigorously stirred solution of the isoflavan (1lb) (120 mg) in pyridine (40 mg) at 190 "C, 3-hydroxyc3-methyl- 1,l-dimethoxybutane ( 14) (50 mg) was added dropwise, a similar addition being made 4 h later.20 The mixture was then heated for a further 10 21, the pyridine was evaporated off, and the two products were isolated by t.1.c. (benzene-ethyl acetate, 99 : 1). One compound (RF 0.65) was obtained as an oil (20 mg), identical with the 2'-methyl ether of natural leiocin (le) (Found: C, 71.8; H, 6.5. C22H22O5 requires C, 72.1; H, 6.1).The mass and n.m.r. spectra were identical with those of the methyl ether of the natural product. 2'-O-Methylisoleio~in (12b). During the synthesis of 2'-O-methyl-leiocin from the isoflavan (1lb) a second compound was produced, which was isolated by t.1.c. (RF 0.53). 2'-O-MethyZisoZeiocin ( 12b) readily crystallized from EtOH as white needles (20 mg), m.p. 130" (Found: C, 71.7; H, 6.3; M+, 366.150. C,,H,,O, requires C, 72.1; H, 6.1; M, 366.147), m/e 366(60(70, M+),351(100), 199(48), 188(3.1), 187(5.8), 186(8.6), 185(39), 179(18.1), 178(61),177(6.4), 176( 63), 175( 61), 174(53), 173(57), 166(29), I 65 (6 1) , 163 (34), 1 53 (23), 15 1 (26), I4 9 (10.5), 145(15.7), 135(30), and 133(52); T 3.33(s, H-5), 3.36(s, H-6'), 3.44(s, H-3'), 3.70(~, H-8), 3.74(d, J 10.0 Hz, H-4"), 4.10(~, OCH2-0),4.54(d, J 10.0 Hz, H-3'7, 5.74(dd, J 10.0 and 4.0 Hz, H-2,,), 6.04(t, J 10.0 and 10.0 Hz, H-2,,), 6.23(s, OCH,), 6.30-6.60(m, H-3), 7.16(d, J 8.0 Hz, H-4), and 8.59(s, 2 x 2"-CH3). 23 F. E. King and T. J. King, J. Chem. Soc., 1951, 569. We thank the South African Council of Scientific and Industrial Research, Pretoria, and the Sentrale Navorsings- fonds of this University for support; also Mr. P. van Wyk, Assistant Director of Research, Kruger National Park, Skukuza for the collection and authentication of bark; Dr. J. M. Steyn, Department of Pharmacology of this Univer- sity, and Dr. K. H. Hall, National Chemical Research Laboratory, C.S. I.R., Pretoria for mass spectra ; Professor G. J. H. Rall and Dr. M. E. Oberholzer of this Department for discussions; and the South African C. S. I. R. for a Special Merit Award to one of us (F. R. v. H.). 7/1142 Received, 30th June, 19773