Xanthones and coumarins from Kielmeyera lathrophyton

Abstracts

Three xanthones and six coumarins were isolated from the hexane extract of the stems of Kielmeyera lathrophyton, among them two new prenylated xanthones 1,5-dihydroxy -6'-methyl -6' -(4-methyl -3-pentenyl) -pyrano(2',3':3,2) -xanthone, 1,7 -dihydroxy -6' -methyl -6' -(4 -methyl -3 -pentenyl) -pyrano(2',3':3,2) -xanthone, and two new 4 -s -butylcoumarins 7 -hydroxy -8 -(3-methyl -1 -oxobutyl) -4 -s -butyl -6',6' -dimethylpyrano (2',3':5,6) -coumarin, 7 -hydroxy -8 -(2-methyl -1 -oxobutyl) -4 -s -butyl -6',6' -dimethylpyrano (2',3':5,6) -coumarin, along with the compounds, delta -tocotrienol, friedelin, 24alpha -ethylcholest -5 -en -3 -one, and , 24alpha -ethylcholest -5,22 -dien -3 -ol. These compounds were identified by comparison with literature data, and their spectroscopic properties.

Kielmeyera lathrophyton; Guttiferae; xanthones; 4-alkylcoumarins; 4-phenylcoumarins; neoflavonoids

Do extrato hexânico de Kielmeyera lathrophyton foram isoladas duas novas xantonas, 1,5 -diidroxi -6' -metil -6' -(4 -metil -3 -pentenil) -pirano(2',3':3,2) -xantona, 1,7 -diidroxi -6' -metil -6' -(4 -metil -3-pentenil) -pirano(2',3':3,2) -xantona. Uma terceira xantona, a 2,3 -metilenodioxixantona, teve a atribuição dos dados de RMN de 13C revista. Foram isoladas ainda seis cumarinas sendo duas delas inéditas, 7 -hidroxi -8 -(3 -metil -1 -oxobutil) -4 -s -butil -6',6' -dimetilpirano(2',3':5,6) -cumarina e 7 -hidroxi -8 -(2 -metil -1 -oxobutil) -4 -s -butil -6',6'dimetilpirano(2',3':5,6) -cumarina. Além dessas substâncias foram isolados ainda o delta-tocotrienol, a friedelina, o 24alfa -etilcolest -5 -en -3 -ona e o 24alfa -etilcolest -5,22 -dien -3 -ol. Estes compostos foram identificados através de suas propriedades espectroscópicas e por comparação de seus dados espectroscópicos com dados da literatura.

Article

Xanthones and Coumarins from Kielmeyera lathrophyton

Frederico G. Cruz^a*, José T. da Silva-Neto^a and Maria L. S. Guedes^b

^a Instituto de Química, Universidade Federal da Bahia, 40170-290, Salvador-BA, Brazil

^b Instituto de Biologia, Universidade Federal da Bahia, 40170-290, Salvador-BA, Brazil

Do extrato hexânico de Kielmeyera lathrophyton foram isoladas duas novas xantonas, 1,5 -diidroxi -6' -metil -6' -(4 -metil -3 -pentenil) -pirano(2',3':3,2) -xantona, 1,7 -diidroxi -6' -metil -6' -(4 -metil -3-pentenil) -pirano(2',3':3,2) -xantona. Uma terceira xantona, a 2,3 -metilenodioxixantona, teve a atribuição dos dados de RMN de ¹³C revista. Foram isoladas ainda seis cumarinas sendo duas delas inéditas, 7 -hidroxi -8 -(3 -metil -1 -oxobutil) -4 -s -butil -6',6' -dimetilpirano(2',3':5,6) -cumarina e 7 -hidroxi -8 -(2 -metil -1 -oxobutil) -4 -s -butil -6',6'dimetilpirano(2',3':5,6) -cumarina. Além dessas substâncias foram isolados ainda o d-tocotrienol, a friedelina, o 24a -etilcolest -5 -en -3 -ona e o 24a -etilcolest -5,22 -dien -3 -ol. Estes compostos foram identificados através de suas propriedades espectroscópicas e por comparação de seus dados espectroscópicos com dados da literatura.

Three xanthones and six coumarins were isolated from the hexane extract of the stems of Kielmeyera lathrophyton, among them two new prenylated xanthones 1,5-dihydroxy -6'-methyl -6' -(4-methyl -3-pentenyl) -pyrano(2',3':3,2) -xanthone, 1,7 -dihydroxy -6' -methyl -6' -(4 -methyl -3 -pentenyl) -pyrano(2',3':3,2) -xanthone, and two new 4 -s -butylcoumarins 7 -hydroxy -8 -(3-methyl -1 -oxobutyl) -4 -s -butyl -6',6' -dimethylpyrano (2',3':5,6) -coumarin, 7 -hydroxy -8 -(2-methyl -1 -oxobutyl) -4 -s -butyl -6',6' -dimethylpyrano (2',3':5,6) -coumarin, along with the compounds, d -tocotrienol, friedelin, 24a -ethylcholest -5 -en -3 -one, and , 24a -ethylcholest -5,22 -dien -3 -ol. These compounds were identified by comparison with literature data, and their spectroscopic properties.

Keywords: Kielmeyera lathrophyton, Guttiferae, xanthones, 4-alkylcoumarins, 4-phenylcoumarins, neoflavonoids

Introduction

Guttiferae is a family generally confined to the tropics. The genus Kielmeyera is endemic to South America¹ with large occurrence in the Brazilian "cerrados" (savannas). Early studies with Kielmeyera species from "cerrado" of the Central Brazilian plateau showed xanthones as principal constituents^2-10. On the other hand, in our recent investigation with Kielmeyera species from "restinga" (sand dunes) of Bahia state coast we have found mainly prenylated 4-phenyl and 4-n-propylcoumarins^11,12.

In the species K. lathrophyton, which was harvested on a "campo rupestre" area in the Chapada Diamantina, Bahia state, a region localized between the coast and the Central plateau, we found beyond xanthones 4-alkyl and 4-phenyl coumarins.

Experimental

UV: CH₃OH and CH₃OH/NaOH. EIMS: Direct probe insert at 70 eV. NMR: Gemini 300-Varian. 241 Perkin-Elmer polarimeter.

Plant material

Kielmeyera lathrophyton, Saady, was collected at Parque Nacional da Chapada Diamantina, Bahia, Brazil, in August 1996. A voucher specimen, N^o 35942, has been deposited in the Alexandre Leal Costa Herbarium, Instituto de Biologia, Universidade Federal da Bahia, Salvador, Brazil.

Extraction and Isolation

Dried stems (5 kg) were extracted with hexane. The extract (80 g) was concentrated under reduced pressure and then submitted to chromatography on silica gel column using hexane-EtOAc gradient. Some fractions were rechromatographed on silica gel CC using hexane-EtOAc gradient to give 1 (0.031 g), 2 (0.006 g), 3 (0.008 g), 4 (0.092 g), 5 (0.023 g), 6 (0.035 g), 7 (0.040 g), 9 (0.122 g), 10 (0.017 g), and a mixture of 8 (70%, 0.083 g) and 3 (30%, 0.036 g).

Compound 1. C₂₃H₂₂O₅, 1,5 -dihydroxy -6' -methyl -6' -(4 -methyl -3 -pentenyl) -pyrano(2',3':3,2) -xanthone . Yellow crystals, mp 142-143^oC (hexane); ¹H and ¹³C NMR, Table 1. EIMS m/z 378 [M]⁺ (6%), 363 (2), 295(100); l_max/nm (MeOH) 238, 268, 294, 312; n_max/cm^-1 3338, 1652, 1613, 1581, 1497, (film CHCl₃); [a]²²_D +2.30 (c 0.4, CHCl₃).

Compound 2. C₂₃H₂₂O₅, 1,7 -dihydroxy -6' -methyl -6' -(4 -methyl -3 -pentenyl) -pyrano(2',3':3,2) -xanthone. Yellow amorphous solid; ¹H and ¹³C NMR, Table 1; EIMS m/z 378 [M]⁺ (20%), 363 (5), 295 (100). l_max/nm (CH₃OH) 223, 253, 285; n_max/cm^-1 3430, 1652, 1613, 1467, (film CHCl₃); [a]²²_D +5.76 (c 0.6 CHCl₃).

Compound 3. C₁₄H₈O₄, 2,3 -methylenedioxyxanthone.¹H and ¹³C NMR, Table 1; EIMS m/z 240 [M]⁺ (100%), 241 (15), 239 (61),149 (8), 126 (13), 105 (9); UV l_max/nm (CH₃OH) 225, 240, 270, 304, 350; n_max/cm^-1 1655, 1632, 1608, 1577, 1466, 935 (film CHCl₃).

Compound4. C₂₃H₂₈O₅, 7 -hydroxy -8 -(3 -methyl -1 -oxobutyl) -4 -s -butyl -6',6' -dimethylpyrano(2',3':5,6) -coumarin. Yellow-greenish amorphous solid; ¹H and ¹³C NMR, Table 3; EIMS m/z 384 [M]⁺ (29%), 369 (100), 341 (21), 327 (12), 313 (9); [a]²²_D +1.82 (c 0.4 CHCl₃).

Compound 5. C₂₃H₂₈O₅, 7 -hydroxy -8 -(2 -methyl -1 -oxobutyl) -4 -s -butyl -6',6' -dimethylpyrano(2',3':5,6) -coumarin. Yellow-greenish amorphous solid; ¹H and ¹³C NMR, Table 3; EIMS m/z 384 [M]⁺ (38%), 369 (100), 341 (14), 327 (49), 313 (6); n_max/cm^-1 3462, 1740, 1614, 1580, 1557, 1383, 1197, 1143, (film CHCl₃); [a]²²_D +0.69 (c 0.5 CHCl₃).

Compound 6. C₂₂H₂₆O₅, 7 -hydroxy -8 -(2-methyl -1 -oxobutyl) -4 -n -propyl -6',6' -dimethylpyrano(2',3':5,6) -coumarin. Yellow-greenish amorphous solid; ¹H NMR (300 MHz, CDCl₃) d 0.97 (t, 3H, 7.3 Hz, H-4''), 1.04 (t, 3H, 7.3 Hz, H-3'''), 1.24 (d, 3H, 6.7 Hz, H-5''), 1.40 (m, 2H, H-3''), 1.52 (s, 6H, H-7' e H-8'), d 1.60 (m, 2H, H-2'''), 2.90 (t, 2H, 7.5 Hz; H-1'''), 3.89 (m, 1H, H-2''), 5.57 (d, 1H, 10.0 Hz, H-5'), 6.72 (d, 1H, 10.0 Hz, H-4'), 6.00 (s, 1H, H-3), 14.45 (s, 1H, 7-OH); ¹³C NMR (75 MHz CDCl₃), d 159.1 (C-2), 110.5 (C-3), 158.3 (C-4), 102.7 (C-4a), 157.1 (C-5), 106.1 (C-6), 163.1 (C-7), 104.1 (C-8), 156.5 (C-8a), 116.0 (C-4'), 126.3 (C-5'), 79.6 (C-6'), 28.2 (C-7'), 28.2 (C-8'), 210.7 (C-1''), 46.9 (C-2''), 27.2 (C-3''), 11.7 (C-4''), 16.5 (C-5''), 39.0 (C-1'''), 23.3 (C-2'''), 13.9 (C-3'''); EIMS m/z 370 [M]⁺ (43%), 355 (100), 337 (25), 313 (71); n_max/cm^-1 3466, 1732, 1557, 1463, 1386, 1145, (film CHCl₃); l_max/nm (CH₃OH) 306; l_max^NaOH/nm (CH₃OH) 384.

Compound 7. C₂₅H₂₄O₅, 5 -hydroxy -6 -(2 -methyl -1 -oxobutyl) -4 -phenyl -6',6' -dimethylpyrano(2',3':7,8) -coumarin. Yellow-greenish amorphous solid; ¹H NMR (300 MHz, CDCl₃) d 0.90 (t, 3H, 7.3 Hz, H-4''), 1.16 (d, 3H, 6.6 Hz, H-5''), 1.40 (m, 2H, H-3''), 1.57 (s, 6H, H-7' e H-8'), 3.74 (m, 1H, H-2''), 5.64 (d, 1H, 10.0 Hz, H-5'), 5.99 (s, 1H, H-3), 6.90 (d, 1H, 10.0 Hz, H-4'), 7.31 (m, 1H, phenyl), 7.40 (m, 4H, phenyl), 14.69 (s, 1H, 5-OH). ¹³C NMR (75 MHz, CDCl₃), 159.5 (C-2), 112.5 (C-3), 154.6 (C-4), 102.1 (C-4a), 164.3 (C-5), 106.8 (C-6), 156.3 (C-7), 101.4 (C-8), 157.7 (C-8a), 115.4 (C-4'), 126.2 (C-5'), 79.7 (C-6'), 28.0 (C-7'), 28.0 (C-8'), 211.3 (C-1''), 46.5 (C-2''), 26.5 (C-3''), 11.7 (C-4''), 16.5 (C-5''), 139.0 (C-1'''), 127.0 (C-2''' and C-6'''), 127.5 (C-3''' and C-5'''), 128.1 (C-4'''). EIMS m/z 404 [M]⁺ (44%), 389 (100), 347 (86); n_max/cm^-1 3448, 1748, 1650, 1582, 1132, 1115, 699 (film CHCl₃); l_max/nm (CH₃OH) 232, 285, 345; l_max^NaOH/nm 250, 313, 433.

Compound 8. C₂₅H₂₄O₅, 5 -hydroxy -6 -(3 -methyl -1 -oxobutyl) -4 -phenyl -6',6' -dimethylpyrano(2',3':7,8) -coumarin. Yellow-greenish amorphous solid; ¹H NMR (300 MHz, CDCl₃) d 0.94 (d, 6H, 6.7 Hz, H-4''), 1.60 (s, 6H, H-7' and H-8'), 2.19 (m, 1H, H-3''), 2.90 (d, 2H, 6.9 Hz, H-2''), 5.60 (d, 1H, 10.0 Hz, H-5'), 5.99 (s, 1H, H-3), 6.90 (d, 1H, 10.0 Hz, H-4'), 7.30 (m, 1H, phenyl), 7.40 (m, 4H, phenyl), 14.73 (s, 1H, 5-OH); ¹³C NMR (75 MHz, CDCl₃) d 159.6 (C-2), 112.6 (C-3), 154.7 (C-4), 102.2 (C-4a), 164.5 (C-5), 106.9 (C-6), 156.4 (C-7), 101.4 (C-8), 157.8 (C-8a), 115.5 (C-4'), 126.2 (C-5'), 79.8 (C-6'), 28.1 (C-7'), 28.1 (C-8'), 206.7 (C-1''), 53.5.5 (C-2''), 25.0 (C-3''), 22.6 (C-4''), 22.6 (C-5''), 139.2 (C-1'''), 127.1 (C-2''' and C-6'''), 127.5 (C-3''' and C-5'''), 128.1 (C-4''').

Compound 9. C₂₂H₂₆O₅, 5 -hydroxy -6 -(2 -methyl -1 -oxobutyl) -4 -n -propyl -6',6' -dimethylpyrano(2',3':7,8) -coumarin. Yellow oil; ¹H NMR (300 MHz, CDCl₃) d 0.89 (t, 3H, 7.5 Hz, H-4''), 0.97 (t, 3H, 7.3 Hz, H-3'''), 1.17 (d, 3H, 6.7 Hz, H-5''), 1.40 (m, 2H, H-3''), 1.51 (s, 6H, H-7' and H-8'), 1.56 (m, 2H, H-2'''), 2.89 (t, 2H, 7.5 Hz, H-1'''), 3.72 (m, 1H, H-2''), 5.56 (d, 1H, 10.0 Hz, H-5'), 6.79 (d, 1H, 10.0 Hz, H-4'), 5.90 (s, 1H, H-3), 15.29 (s, 1H, 5-OH). ¹³C NMR (75 MHz, CDCl₃) d 159.6 (C-2), 110.1 (C-3), 159.2 (C-4), 103.1 (C-4a), 165.1 (C-5), 106.7 (C-6), 157.1 (C-7), 101.4 (C-8), 154.9 (C-8a), 115.5 (C-4'), 126.1 (C-5'), 79.5 (C-6'), 27.9 (C-7'), 27.9 (C-8'), 211.7 (C-1''), 46.5 (C-2''), 26.6 (C-3''), 11.7 (C-4''), 16.6 (C-5''), 38.3 (C-1'''), 22.6 (C-2'''), 13.8 (C-3'); EIMS m/z 370 [M]⁺ (35%), 355 (100), 337 (33), 313 (23); n_max/cm^-1 3489, 1748, 1614, 1581, 1189, 1146, 1113 (film CHCl₃); l_max/nm (CH₃OH) 227, 287, 337; l_max^NaOH/nm 247, 312, 413.

Results and Discussion

From the hexane extract of the stems of K. lathrophyton we isolated two new prenylated xanthones, 1 and 2, and two new 4-s-butylcoumarins, 4 and 5, along with the known 2,3-methylenedioxyxanthone 3¹³, 7-hydroxy-8-(2-methyl-1-oxobutyl)-4-n-propyl-6',6'-dimethylpyrano (2',3':5,6)- coumarin 6¹⁴, 5 -hydroxy- 6- (2 -methyl -1 -oxobutyl) -4 -phenyl-6',6' -dimethylpyrano (2',3':7,8) -coumarin 7^14,15, 5 -hydroxy -6 -(3 -methyl -1 -oxobutyl) -4 -phenyl -6',6' -dimethylpyrano (2',3':7,8) -coumarin 8^10,14-16, 5 -hydroxy -6 -(2 -methyl -1 -oxobutyl) -4 -n -propyl -6',6' -dimethylpyrano (2',3':7,8) -coumarin 9¹⁴, d -tocotrienol 10¹⁷, friedelin¹⁸, 24a -ethylcholest -5 -en -3 -one, and, 24a -ethylcholest -5,22 -dien -3 -ol¹⁹. Compound 6 was previously reported as a synthetic product¹⁴. The molecular formulae of these compounds were determined by EI mass spectrometry and by ¹H and ¹³C NMR.

Xanthone 1, yellow crystals, mp 142-143^oC, has the molecular formula C₂₃H₂₂O₅. The UV spectrum showed absorptions at 238, 268, 294, and 312 nm, and its IR spectrum showed absorptions at 3338, 1652, 1613, and 1581 cm^-1, suggesting the xanthone skeleton with a chelated hydroxyl group^6,21. Both the ¹H and ¹³C NMR spectra (Table 1) revealed the presence of a prenyl moiety characterized by the signals at d 5.09 (bt, 6.9 Hz, H-10'), 1.57 (s, H-13'), 1.66 (s, H-12'), 132.0 (C-11'), 123.6 (C-10'), 17.6 (C-13'), 25.7 (C-12'), and 22.6 (C-9'). The presence of a chromene ring system was indicated by an AX proton system at d 5.56 (d, 10.0 Hz, H-5') and 6.76 (d, 10.0 Hz, H-4') and by the signals at 126.5 (C-5'), 115.8 (C-4'), 81.0 (C-6'), and 27.7 (C-7'). The lack of one methyl group signal, that would be necessary for the 6',6'-dimethylchromene system and the appearance of one addtional methylene signal at d 41.7 (C-8'), suggested that one methyl group was substituted by a 4-methylpent-3-enyl group. This fact was corroborated by the appearance of an abundant fragment ion at m/z 295 ([M]⁺ - 83) resulting from the loss of the 4-methyl-3-pentenyl moiety. The analysis of an aromatic ABC type proton system at d 7.24 (t, 8.0 Hz, H-7), 7.32 (dd, 8.0, 1.7 Hz, H-6), and 7.75 (dd, 8.0, 1.7 Hz, H-8), suggested the presence of three adjacent protons. A shielded isolated proton at d 6.36 (s, H-4) was in agreement with a pentasubstituted aromatic A ring. The presence of a conjugated carbonyl and a chelated hydroxyl were confirmed by the signals at d 180.7 (C-9) and 13.16 (s, 1-OH), respectively. The long range correlations (Table 2) of the signal at d 13.16 (s, 1-OH) with the signals at d 157.8 (C-1), 104.8 (C-2), and 103.8 (C-9a), jointly with the correlations of the signal at d 6.36 (H-4) with d 161.3 (C-3), 156.3 (C-4a) and 104.8 (C-2) and that of d 5.56 (H-5') with d 104.8 (C-2) allowed an unequivocal assignment of the A ring in the xanthone moiety. In the B ring, the deshielded signal of H-8 at d 7.75 indicated a periplanar relation with the carbonyl. The long range correlations of H-8 with the signals at d 144.2 (C-5a) and 121.1 (C-8a) and those of the signal at d 7.24 (H-7) with d 144.3 (C-5), established the hydroxyl position at C-5. The unequivocal assignments of carbons C-6, C-7, and C-8 were made by a ¹H-¹³C COSY (J = 140 Hz) experiment.

Xanthone 2 had the same molecular formula as xanthone 1, C₂₃H₂₂O₅, and showed similar UV, IR, and MS data. Nevertheless their ¹H NMR spectra (Table 1), showed significant differences in the aromatic region. The presence of a 1,2,4 ABC type proton system in 2 was deduced by the signals at d 7.25 (dd, 9.0; 3.0 Hz, H-6), 7.33 (d, 9.0 Hz, H-5), and 7.59 (d, 3.0 Hz, H-8). The long range correlations (Table 2) allowed an unequivocal assignment of the B ring and confirmed the structure proposed.

The 2,3-methylenedioxyxanthone 3 has been already isolated from Hypericum mysorense Heyne¹³, but because of some divergences in the ¹³C NMR data attribution, we made a reassignment. In the ¹H NMR spectrum (Table 1), the presence of two singlets at d 6.89 (H-4) and 7.64 (H-1), and other four aromatic proton signals at d 7.44, (d, 8.0 Hz, H-5), 7.68 (td, 1.5; 8.0 Hz, H-6), 7.36 (t, 8.0 Hz, H-7), and 8.31 (dd, 1.5; 8.0 Hz, H-8) established a disubstituted xanthone with a methylenedioxy group, d 6.12 (s, H-10), at 2,3 positions.

The ¹³C NMR spectrum (Table 1) showed five deshielded signals at d 175.7, 156.0, 153.7, 153.6 and 145.3, that were assigned to carbons C-9, C-5a, C-4a, C-3 and C-2, respectively.

The ¹H-¹H COSY and the long range correlations showed by the ¹H-¹³C COSY (J 9 Hz) (Table 2) confirmed the assignments for compound 3. The correlations between the signal at d 7.64 (H-1) with signals at d 153.6 (C-3) and 153.7 (C-4a) and those of the signal at d 6.89 (H-4) with signals at d 116.6 (C-9a) and 145.3 (C-2) substantiate the proposed structure.

Both compounds 4 and 5 have molecular formula C₂₃H₂₈O₅, deduced by EIMS (M⁺ = 384) and ¹³C NMR. Spectral data suggested for both 4 and 5 the 4-alkylcoumarin skeleton with a chelated hydroxyl^{14, 15}. They showed very similar ¹H and ¹³C NMR data and structurally differ only in the C-8 acyl side chain. The ¹H NMR spectra (Table 3) of these compounds showed signals for the 6',6'-dimethyl-chromene ring, a H-3 singlet, one hydrogen of chelated hydroxyl, one acyl side chain and a 4-s-butyl group.

In compound 4, the 4-s-butyl group was characterized by the multiplet at d 3.84, 1H (H-2'''), a doublet at d 1.24, 3H (H-1'''), a multiplet at d 1.77, 2H (H-3''') and a triplet at d 0.97, 3H (H-4'''), in the ¹H NMR spectrum, and by the signals at d 37.5 (CH, C-2'''), 20.0 (CH₃, C-1'''), 29.5 (CH₂, C-3''') and 11.8 (CH₃, C-4''') in the ¹³C NMR spectrum, while the 3-methyl-1-oxobutyl side chain was characterized in the ¹H NMR spectrum by a doublet at d 3.15, 2H (H-2''), a multiplet at d 2.30, 1H (H-3''), a doublet at d 1.02, 6H (H-4'' and H-5'') and in the ¹³C NMR spectrum by the signals at d 206.3 (C=O, C-1''), 53.6 (CH₂, C-2''), 25.6 (CH, C-3'') and the methyl groups at d 22.6 (C-4'' and C-5'').

The locations of the substituents around the aromatic coumarin ring are supported by long range correlations (Table 4) and nOe experiments. The long range correlations of the signal at d 6.13 (H-3) with the resonances at d 102.8 and 159.6 permitted assignment of these signals to C-4a and C-2, respectively. In accordance with the accepted neoflavonoid oxidation pattern^{14, 20}, carbons C-5 and C-7 of the aromatic ring are oxygenated, thus the correlations of the hydrogen at d 14.49 with the resonances at d 104.7 (C-8), 106.2 (C-6), and 162.9 (C-7) and the correlation of the signal at d 6.74 (H-4') with the signal at d 157.3 (C-5) allowed location of the OH at C-7 and the 6',6'-dimethylchromene ring at C-5 and C-6. Consequently the 3-methyl-1-oxobutyl group was placed at C-8. By exclusion, the s-butyl group was located at C-4. This assumption was corroborated by the enhancement of the signal at d 1.24 (H-1''') in the NOEDIF experiment when H-3 (d 6.13) was irradiated.

The analysis of the ¹H NMR spectrum of compound 5 was more complicated due the overlap of three pairs of hydrogen signals of the s-butyl and 2-methyl-1-oxo-butyl groups. However, these signals were unambiguously assigned with the help of the one bond ¹H – ¹³C COSY spectrum (Table 3). This spectrum showed correlations of the multiplet at d 3.89, 2H, with the signals at d 46.9 (C-2'') and 37.5 (C-2'''), of the triplet at d 0.97, 6H, with the signals at d 11.8 (C-4'') and 11.7 (C-4''') and of the doublet at d 1.25, 6H, with the signals at d 16.6 (C-5'') and 20.0 (C-1'''). The signals at d 46.9 (CH), 16.6 (CH₃), 11.8 (CH₃), 210.8 (C=O) and 27.2 (CH₂) were assigned to the 2-methyl-1-oxobutyl group, while the signals at d 37.5 (CH), 20.0 (CH₃), 11.7 (CH₃) and 29.5 (CH₂) were assigned to the s-butyl group. The analysis of the long range correlations spectrum (Table 4) facilitated the location of a hydroxyl group at C-7, of the 2,2-dimetylchromene ring at C-5 and C-6 and of the 2-methyl-1-oxobutyl group at C-8. The s-butyl group was located at C-4 due the observed long range correlation between the signal at d 1.25 (H-1''') and the signal at d 164.2 (C-4) and by the enhancement of the signal at d 1.25 (H-1''') in the NOEDIF experiment when H-3 (d 6.13) was irradiated.

The structures of the known compounds 6, 7, 8, and 9 were determined by a combination of IV, UV, EM, ¹H and ¹³C NMR, DEPT, ¹H – ¹H COSY and ¹H – ¹³C COSY (one bond and multiple bonds) data. This is the first time that their ¹³C NMR signals assignments are reported (Experimental section).

Acknowledgments

The authors are grateful to João Lago (IQ-USP) for recording the a_D values, to Roy Funch from Fundação Chapada Diamantina (Lençois) for providing local support during the plant collect, as well as to CAPES for the MSc fellowships to JTSN. This work was supported by grants from CNPq and FINEP.

Received: February 11, 2000

Published on the web: November 29, 2000

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Publication Dates

• Publication in this collection
  19 Apr 2001
• Date of issue
  2001

History

• Received
  11 Feb 2000