Further Diterpenoids Isolated from Pterodon polygalaeflorus

Dos frutos de Pterodon polygalaeflorus (Leguminosae) foram isolados o novo diterpeno 6 αhidroxivouacapano e os conhecidos diterpenóides 6 α,7β,14β,19-tetraidroxivouacapano, 6 α,7βdiidroxivouacapan-17 β-oato de metila e o flavonóide taxifolina. As estruturas foram determinadas com base em análise espectroscópica, inclusive RMN bidimensional, transformação química do novo diterpeno e comparação com dados da literatura.

Compound 1 was obtained as colorless needles after crystallization from methanol.The HREIMS spectrum showed the molecular ion at m/z 302.2126 corresponding to the molecular formula C 20 H 30 O 2 (m/z 302.2238, ∆m/z = 0.0112 daltons).This data together with the presence of signals for three quaternary [δ H 0.89 (s,3H-20), 1.07(s, 3H-19) and 1.17 (s, 3H-18)] and one tertiary [δ H 0.99 (d, J=6.9 Hz, 3H-17)] methyl groups, one carbinolic hydrogen at δ H 3.94 (td, J=7.1, 3.6 Hz, H-6) and two hydrogens at δ H 6.17 (d, J=1.6 Hz, H-15) and 7.20 (d, J=1.6 Hz, H-16) of a 2,3-disubstituted furan observed in the 1 H NMR spectrum allowed us to classify this diterpene as a vouacapanoid, the same class of diterpenoids which was reported previously 1 .This deduction was confirmed by comparative analysis of the HBBD-and DEPT- 13  (δ H 0.91)] and via long range coupling CH [ 13 Cx 1 H-COSYn J CH (n = 2 and 3) COLOC]: δ C 60.02 (C-5) correlated with 3H-18 (δ H 1.17)] spectra.Additional confirmation of the presence of a hydroxyl group at C-6 was obtained from the 13 C NMR spectrum of the acetyl derivative of 1a: i) the The 2D carbon-hydrogen correlation experiments modulated with 1 J CH established the hydrogen chemical shift correlations with those of the carbon atoms and also 2 J CH and 3 J CH couplings to detect hydrogen resonance correlated with not directly bound carbon signals, along with the application of the usual shift parameters and multiplicity of signals, were used to complete the assignment of the 1 H and 13 C NMR spectra of 1 (Table 2).
Confirmation of 1 as a natural product (and not as a hydrolysis product) was obtained by preparation of a new hexane extract from fruits (1.5 kg) collected from the same specimen.The residue (16 g) was submitted to column chromatography on silica gel eluted with hexane, CHCl 3 and EtOAc.The residue (5.3 g) from the CHCl 3 elution was submitted to a preparative TLC affording 1 (12.7 mg).
The relative configuration of 1 was also deduced on the basis of the [α] D = + 26.6 ± 0.05 (c 1.0, CHCl 3 ) compared with value described in the literature for this compound obtained of the acetyl derivative 1a by treatment with LiAlH 4 7 .

Extraction and isolation of the constituents
The powdered fruits (5 kg) were extracted with hexane in a Sohxlet apparatus to yield 500 g of a yellowish oil that was designated EH.The yellowish oil EH (100 g) was submitted to alkaline hydrolysis according to usual procedure, KOH-H 2 O-EtOH (1:1) under reflux for 30 min.Column chromatography of the ppt (60 g) obtained after addition H Acetylation of 1 6α-Acetoxyvouacapane (1a) was obtained by treatment of 1 (105 mg) with Ac 2 O (5 mL) and pyridine (1.5 mL).The usual work-up followed by CC on silica gel [hexane:CHCl 3 1:1 as eluent] of the crude product furnished 1a (100 mg) as an oil fr.homogeneous by TLC. 1 Mps: uncorr.Optical rotation was obtained on a Perkin-Elmer 341 digital polarimeter; NMR: 1 H(200 MHz) and 13 C (50.3 MHz) in CDCl 3 (1 and 2), CDCl 3 + acetone-d 6 (3 and 4) and TMS as int.standard; EIMS: 70 eV.;CC: silica gel (Merck 0.05-0.20 mm); TLC: silica gel H or G (Merck) and spots were visualized by exposure to iodine vapour.Plant material Pterodon polygalaeflorus Benth.was collected in May 1993 in Joaquim Pires, Piauí State, Brazil.A voucher specimen (N o 8808) representing the collection was identified by Dr Afranio G. Fernandes (Botanist, Departamento de Biologia, UFC) and has been deposited at Herbario Prisco Bezerra of the Departamento de Biologia, Universidade Federal do Ceará, Brazil.

Table 1 .
1H (200 MHz) and 13 C (50.3 MHz) NMR spectral data for diterpenes 2, 2a and 2b in CDCl 3 and TMS as internal standard, including 1 J CH (fully coupled) of 2 obtained by gated experiment.* *Multiplicity of signals of carbon atoms deduced by comparative analysis of HBBD-and DEPT-13 C NMR.Chemical shifts and coupling constants of hydrogen atoms obtained from 1 H NMR.