Fabaceae is one of the largest plant families consisting of about 730 genera and 14,900 species identified to date . The genus Dalbergia belongs to the Faboideae sub-family and consists of 274 species distributed across the globe  . Most of the species from this genus are timber trees including Dalbergia lanceolaria, the plant investigated here. It is tall deciduous tree distributed in Bangladesh, Bhutan, India, Sri Lanka, Myanmar, Thailand, Cambodia, Vietnam and Pakistan . Its root bark is used by local population for dyspepsia and the leaves are used for skin disorders such as leprosy . Oil extracted from its seeds is used for rheumatic and skin disorders .
Multiple studies have evaluated the biological activities of D. lanceolaria extracts and provided proof of anti-inflammatory, analgesic, and anti-diarrheal activity   . Only one study is available which investigated chemical constituents from the root barks and identified a new glycoside—namely Lanceolarin . A large number of compounds have been identified from various other species of Dalbergia genus. Flavonoids were the most common type of compounds isolated, and some terpenes have also been identified  . However, no alkaloid has been reported to date. Among the terpenes, triterpenes and sesquiterpenes are common but diterpenes have not been reported.
2. Materials and Methods
2.1. Plant Collection and Identification
For this study, the stem bark of the plant was collected from Chittagong Hill Tracts, Chittagong Division of Bangladesh. Plant was positively identified at Bangladesh National Herbarium and a voucher specimen was deposited for future reference (DACB Accession No. 43435).
2.2. Preparation of Plant Extract
Collected stem bark (3.5 kg) of D. lanceolaria was shed dried for 7 days and then pulverized by a high-capacity grinder to produce fine powder. 1.3 kg of the fine powder was soaked in 5 L of Methanol for 14 days and at the end of the 14-days soaking period, the methanol was evaporated in a rotary evaporator (Rotavapr, Butch, Switzerland) to procure 62.5 gm of crude extract. This crude extract was partitioned between methanol and dichloromethane. After partitioning and subsequent evaporation, 6.88 gm of CH2Cl2-soluble fraction was obtained.
2.3. Chromatographic Separation
The CH2Cl2-soluble fraction was further fractionated using vacuum liquid chromatography (VLC) technique as described in literature . For this purpose, VLC-grade Kieselgel 60H Silica was used as the stationary phase. 6.4 gm of the fractionation was mixed with 35 gm of the stationary phase and placed on top of the packed column. Initially petroleum ether was used as the mobile phase and the fractionation was performed by progressively increasing solvent polarity with the addition of CH2Cl2 (up to 100%), followed by addition of ethyl acetate (up to 100%), and finally methanol (up to 100%). A total of 40 sub-fractions were collected from VLC separation of CH2Cl2-soluble fraction. The sub-fractions were grouped by their TLC profiles and then further separated using LH20 Sephadex column chromatography with the mobile phase system starting with petroleum ether-chloroform (1:4) to 100% chloroform and ending with 100% methanol. This process afforded four compounds (compounds 1-4) which were further purified by preparative TLC.
Compound 1 (Figure 1) was obtained as a yellowish amorphous powder. The molecular formula was determined to be C20H22O7 from NMR data. The 1H NMR spectrum (Figure 2) of 1 showed peaks at peaks at δH 6.65, 7.70, and 7.75 which is indicative of protons in a furan ring. This spectrum also showed peaks at δH 3.93 and 3.63 indicating H-2 and H-3 in an epoxide ring. Singlet peaks at δH 1.11 and 1.04 were deduced to be from the two methyl groups (Me-18 and Me-20) and peak at δH 5.00 was deduced to be from H-1 near the ether bridge. The complete structure was elucidated by the combination of 1H NMR, 13C NMR, DPT-135, 1H-1H COSY, HMBC data and was found to be in agreement with those reported for Jateorin  .
Compound 2 (Figure 3) was obtained as yellow crystalline solid. The molecular formula of this compound was determined to be C20H22O6 from the NMR data. Similar to 1, the spectrum showed peaks at δH 6.46, 7.46, and 7.50 indicating presence of a furan ring. Singlet peaks at δH 1.28 and 1.10 corresponds to methyl groups. Presence of an ether bridge was indicated by a doublet peak at δH 5.18 corresponding to H-1. The complete structure was elucidated by evaluating 1H NMR (Figure 4) and 13C NMR data. The data was in agreement with previous literature reporting Columbin .
Compound 3 (Figure 5) was obtained as colorless needle-shaped crystals. 1H NMR spectrum (Figure 6) showed peaks at δH 3.51 (m, 1H), 5.34 (t, 1H), 0.92 (d, 3H, J = 6.48), 0.81 (d, 3H, J = 6.12), 0.785 (d, 3H, J = 6.54), 0.67 (s, 3H), 0.998 (s, 3H). The structure was elucidated from this data and was compared with previous literature reporting β-sitosterol . Compound 4 (Figure 7) was white amorphous powder. 1H NMR spectral data (Figure 8) from this compound gave peaks at δH 3.18 (dd, 1H), 2.36 (m, 1H), 1.91 (m, 1H), 0.94 (s, 3H), 0.75 (s, 3H), 0.82 (s, 3H), 1.02 (s, 3H), 0.91 (s, 3H), 0.77 (s, 3H), 4.56 (m, 1H), 4.68 (m, 1H), and 1.67 (s, 3H). This data was in agreement with those reported for Lupeol .
Figure 1. Elucidated structure of Compound 1.
Figure 2. 1H NMR spectrum of Compound 1. The spectrum was taken in Bruker 400 MHz NMR instrument using dimethyl sulfoxide (DMSO) as the solvent.
Figure 3. Elucidated structure of Compound 2.
Figure 4. H NMR spectrum of Compound 2. The spectrum was taken in a Bruker 400 MHz NMR instrument using deuterated chloroform (CDCl3) as the solvent.
Figure 5. Elucidated structure of Compound 3.
Figure 6. H NMR spectrum of Compound 3. This spectrum was taken from a Bruker 400 MHz NMR instrument using deuterated chloroform (CDCl3) as the solvent.
Figure 7. Elucidated structure of Compound 4.
Figure 8. H NMR spectrum of Compound 4. This spectrum was taken using a Bruker 400 MHz NMR instrument using deuterated chloroform (CDCl3) as the solvent.
Both β-sitosterol and Lupeol have been previously reported from D. hainanensis, D. latifolia, D. ecastophyllum, and D. miscolubium    . In addition, β-sitosterol has been isolated from other species of Dalbergia genus such as D. rubiginosa, D. volubilis, D. sissoides, and D. sissoo    .
Furanoditerpenes are found in various plants within the Fabaceae family    . However, diterpenes have not been reported for Dalbergia genus except for some Gibberelins identified in D. dolichopetala . Compound 1 (Jateorin) and Compound 2 (Columbin) are furanoditerpenes which is a novel finding for this genus. To the best of the authors’ knowledge, furanoditerpenes have never been reported in any publication for this genus. So, this finding is very interesting with respect to the phytochemistry of this species and the genus as a whole. Furthermore, all four compounds are being reported for the first time for D. lanceolaria.
In this present study, four compounds namely Jateorin, Columbin, β-sitosterol, and Lupeol were isolated from the methanolic extract of stem bark of D. lanceolaria. Among them, β-sitosterol and Lupeol are triterpenes and have been reported from other species within this genus. However, Jateorin and Columbin have not been reported previously from this genus. Hence, it is the recommendation of the authors that a systematic search be initiated to evaluate the presence of furanoditerpenes in other species within the Dalbergia genus.
The authors acknowledge that this investigation was funded by National Science and Technology Fellowship, Ministry of Science and Technology, People’s Republic of Bangladesh.
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