Tetranortriterpenoids and Dihydrocinnamic Acid Derivatives from Hortia colombiana

Dois tetranortriterpenos, sendo um inédito e dois novos derivados do acido dihidrocinâmico foram obtidos da madeira de Hortia colombiana. Suas estruturas foram elucidadas por RMN, e as configurações relativas estabelecidas através de experimentos de nOe diferencial. Em adição, foram isolados aloxantoxiletina, nerolidol, epoxinerolidol, três conhecidos derivados do acido dihidrocinâmico e duas amidas.


Introduction
The Rutaceae family is a source of alkaloids, coumarins, flavonoids and limonoids. 1During a search on Colombian Rutaceae we reported earlier 2 the alkaloidal components isolated from the bark and wood of Hortia colombiana, collected in the Chocó Department (Colombia), one of the most humid regions of the world. 3etailed examination of the wood extract allowed now the isolation of five dihydrocinnamic acid derivatives, two sesquiterpenes, one coumarin, two amides and two limonoids.One tetranortriterpenoid and two of the dihydrocinnamic acid derivatives are new compounds.This paper deals with the isolation of the above secondary metabolites and the structural elucidation of the new compounds.
Compounds 1-3 have been previously reported [4][5][6] from other Hortia spp, while the acid 4 and its methylester 5 are novel compounds.Unequivocal assignement of the 13 C NMR parameters of compounds 1-5 were obtained by HETCOR and Long-range HETCOR experiments, and are reported in Table 1.The data for 1 are coincident with those previously reported, 5 whilst the assignments of the C-6, C-8 and C-9 signals for 3 have been corrected with respect to the literature 6

on the basis of selective INEPT experiments (see Experimental).
The ¹³C NMR data of 2 are here reported for the first time and it should be underlined that the value (δ 19.0) for carbon 3 is quite different from the corresponding values (δ 24.7-25.1)for the other derivatives (Table 1) due to the adjacent aromatic ring ortho-dioxigenation.
In the 1 H NMR spectrum the ester 5 exhibited signals for an aromatic proton, a chromene moiety and two aromatic methoxy group suggesting it is an isomer of 2. Only one of the methoxyls (δ C 62.2; δ H 3.71) was orthodisubstituted 7,8 and in the selective INEPT experiments, the irradiation of the benzylic methylene signal (δ 2.88) gave response, inter alia, for the protonated aromatic carbon (δ 113.1) leaving only the structures 5 or 6 for the compound.The structure 5 was definitively established by difference nOe experiments.Irradiation of the methylene signal (δ 2.88) gave nOe effects on both the aromatic proton and the 5-OMe (δ 3.71) signals, while irradiation at δ 3.71 enhanced the same methylene and H-1' (δ 6.55); on the contrary, the irradiation at δ 3.82 (8-OMe) showed a nOe effect only on the aromatic proton.
Alloxanthoxyletin (7) exhibited in the 1 H NMR spectrum the appropriate signals for a coumarin (δ H 7.96 and 6.12) with a methoxy group (δ C 55.9) and a chromene ring.The other three possible known isomeric coumarin structures, 9 i.e. xanthoxyletin, luvangetin and braylein, were discarded due to either the presence of an ortho-disubstituted OMe (xanthoxyletin and luvangetin) or to the absence of any oxygenated substituent on C-5 (braylein). 10rolidol, 8, epoxynerolidol, 9, as well as the amides 10 11 and 11 were identified on the basis of their NMR spectral data (see Experimental).
The structure 12 for the isolated limonoid named Hortiolide A was initially established by MS and NMR data, subsequently confirmed by single-crystal method. 12he detailed analysis of the spectral data is reported here.Hortiolide A was obtained as a dextrorotatory solid and assigned the molecular formula C 27 H 32 O 7 on the basis of EIMS and NMR evidences.The intense ion at m/z 372 (M + -C 5 H 4 O 2 ) is characteristic of limonoids possessing a furan ring attached to the α, β-unsaturated lactonic D ring. 13he presence of the furan ring was confirmed by the characteristic signal patterns in the 1 H NMR and appropriate carbon signals in 13 C NMR spectra.The assignment of each NMR signal to the pertinent proton and carbon was achieved by HETCOR measurements, while that of quaternary carbons followed from the longrange correlations and are reported in Table 2.In addition, important H-C long-range correlations were obtained by selective INEPT experiments (Table 3).
Examination of the NMR data, mainly the long-range correlations, indicated that, in addition to the furan moiety, hortiolide A contained well-defined A, C and D rings as depicted in 12. Finally, for ring C, important correlations were found between H-9 (δ H 2.80 dd; δ C 45.9) and C-1 and Me-19.Cumulatively, the above data led to the structure 12 for hortiolide A, which was definitively confirmed by an X ray diffraction study. 12o the oily Hortiolide B, C 27 H 30 O 8 , i.e. containing one oxygen and one unsaturation or cycle more than hortiolide A, was assigned the structure 13.The unequivocal assignments of NMR signals are reported in Tables 4 and  5, as a result of 1D-and 2D-NMR experiments.Comparison with the data of hortiolide A suggested the presence of furan and the same D ring.
Upon treatment with acetic anhydride and pyridine the compound was recovered unaltered suggesting the extra oxygen may be part of an epoxide.In accordance, in the 13 C NMR spectrum there are a singlet at δ 116.6 and a doublet at δ 70.6, the latter 1 J correlated to a singlet at δ 5.26, which were attributed to the hemiacetalic C-1 and to the epoxidic C-2, respectively.Accordingly, long-range correlations were found between C-1 and Me-19 (Table 3), and between H-2 and C-1 (Table 4).The trisubstituted  4 and 5) agreed with the proposed structure 13.Assignements of the relative configurations at the seven chiral centers were established by difference nOe experiments.Thus, the selective irradiation at δ 1.42 (Me-18) enhanced the signal for Me-30, and irradiation at δ 1.55 (Me-19) gave responce for Me-28 and the methylene on position 6 (α side of the molecule); while the selective irradiation at δ 2.88 (H-5) enhanced both signals attributed to H-2 and Me-29 (β side), giving further support to the structure 13.
The occurrence of tetranortriterpenoids is limited to the Rutales order comprising Meliaceae, Cneoraceae, Rutaceae and Simarubaceae. 1 This class of compounds is biogenetically derived from ∆ 7 -euphol/tirucallol by oxidative degradation of the C-17 side chain resulting in the loss of four carbon atoms and formation of the β-substituted furan.5][16] The structural variations of limonoids found in Rutaceae are less than in Meliaceae and are generally limited to the modification of A and B rings. 1 It is whortnoting that only one tetranortriterpenoid has previously been reported from the genus Hortia. 5Hortiolide A and B represent new structural types, which may be biogenetically derived from B ring seco limonoids of the so called Group 4. 16 In addition, both have the rare 1,8epoxy linkage, which has been noted before in Utilin C 17 isolated from Meliaceae.

Table 5
3, H-11 showed3J correlations with C-8 and C-13, and 2 J correlations with C-9 and C-12; in turn, the methylene on position 12 (δ C 42.0; δ H 2.37 dd and 2.18 dd) was correlated to C-9 and C-17.On the other side, in the long-range HETCOR spectrum, C-9 showed a cross peak with the Me-19.Other long-range correlations (Tables