Phenolic compounds from the rhizome of Renealmia nicolaioides Loes . : a new diarylheptanoid

This study aims to identify phenolic compounds in dichloromethane and methanolic extracts of the rhizome of Renealmia nicolaioides collected in the North Region of Brazil. Two known diarylheptanoids, 1,7-bis(4-hydroxyphenyl)-(1e)-1-hepten-3-one (1), and 5R-1,7-bis(4-hydroxyphenyl)1e-hepten-5-ol (2), and a new one (1R,2S,5S)-2-hydroxy-1,7(p-hydroxyphenyl)-centrolobine (3), as well as one flavonoid, 3-metoxi-quercetin (4) were isolated by chromatographic procedure and identified by spectroscopic techniques (1h and13C NmR, hRmS and CD). The acetyl derivative of 2 was used to confirm its structure. All four compounds are reported for the first time for this genus, and this is the first occurrence of compound 1 as a natural metabolite. The results reported here are unprecedented for the genus Renealmia.


INTRODUCTION
The genus Renealmia l.f.belongs to the family Zingiberaceae, subfamily Alpinioideae, and tribe Alpinieae, and contains approximately 75 species distributed throughout tropical regions of the Americas and Africa (maas 1977).In Brazil, the genus is represented by 21 species distributed throughout several regions and phytogeographical domains of the country including Amazonia, Caatinga, Cerrado, Atlantic Forest, Pampa, and the Pantanal (maas and maas 2015).Some species of Renealmia are used for medicinal purposes, with anticancer activity and snakebite treatment being the most notable (Negrelle 2015).
Flavonoids isolated from roots of R. nicolaioides induced quinone reductase enzyme phase II, which acts in the protective mechanism against tumor action in hepatocytes (Gu et al. 2002).Flavonoids and diarylheptanoids isolated from the ethanolic extract of R. thyrsoidea rhizome acted against the amastigote form of Leishmania amazonensis (Cabanillas et al. 2014).Pinostronbin, a flavanone isolated from leaves of R. alpinia, inhibited enzymatic and biological activities of PlA2, which is the most abundant and important constituent of snake venoms (Gómez-Betancur et al. 2016).
Among the compounds isolated from Renealmia spp., phenols stand out.Thus, this work aims to identify the phenolic compounds present in the rhizome of R. nicolaioides.

PlANT mATeRIAl
Rhizomes of R. nicolaioides were collected in June 2015, at the Catuaba experimental Farm and the humaitá Forest Reserve, both located in Rio Branco, state of Acre.The material was identified and a voucher (No. 6646) was deposited in the herbarium of the Universidade Federal do Acre (UFACPZ).
eQUIPmeNT One-and two-dimensional 1 h and 13 C nuclear magnetic resonance (NmR) spectra were obtained using a Bruker NmR spectrometer [400 and 500 mhz ( 1 h), 100 and 125 mhz ( 13 C)], using tetramethylsilane (TmS) as internal standard for chemical shift reference.high-resolution electrospray ionization mass spectrometry (eI-hRmS) using a quadrupole-time-of-flight mass spectrometer (XeVO-QToF) was used to obtain the mass spectra.high-performance liquid chromatography (hPlC) measurements were performed using an instrument equipped with a lC-10AS pump, a SPD-10A detector, a CBm-20A-Comunications module (Shimadzu), and a Rheodyne injector with loop of 500 µl.Optical rotation was performed using a JASCO PTC 203 digital polarimeter and a JASCO J-815 CD spectrometer.

eXTRACTION AND ISOlATION
Air-dried powdered rhizomes (155 g) were successively extracted with Ch 2 Cl 2 and Ch 3 Oh at room temperature.Three extractions were made with dichloromethane, while the extraction with the methanol was exhaustive.The periodicity of solvent exchange was on average 48 hours, and each solution was concentrated on a rotary evaporator under vacuum.This process yielded two extracts: dichloromethane rhizome (RNRD) and methanol rhizome (RNRm).
Compound 1, which is a bisdemethoxycurcumin derivate, is being described for the first time from a natural source, although it had been previously synthesized (Jirásek et al. 2014).
Diarylheptanoid 2 has been detected in rhizomes of Curcuma species (Zingiberaceae) C. comosa Roxb., C. elata Roxb.and C. kwangsiensis S.K. lee & C.F. liang.This compound has been shown to exhibit antiallergic activity, potent cytotoxic activity against both the KB and NCI-h187 cell lines, and inhibitory activity for melanogenesis, and may be used in the treatment of skin diseases (li et al. 2010(li et al. , matsumoto et al. 2013(li et al. , 2015(li et al. , Chokchaisiri et al. 2014)).
Flavonoid 4 was isolated from the rhizome of R. nicolaioides.Other flavonoids have also been isolated from the roots of R. nicolaioides (Gu et al. 2002), the leaves of R. thyrsoidea, R. cernua and R. alpinia (Cabanillas et al. 2014, Gilli et al. 2014, Gómez-Betancur et al. 2014, 2015), and from the rhizome of R. thyrsoidea (Cabanillas et al. 2014).Flavonoids are used as chemosystematic markers for the Zingiberaceae (lima and Kaplan 2010), and are commonly found among its genera.
The occurrence of the diarylheptanoids 1 and 2 in four different fractions from the rhizome of R. nicolaioides could be potential chemotaxonomic markers for this species.Further phytochemical studies with other species of Renealmia are needed to fully understand the chemosystematic significance of these compounds for this genus.Compound 3 can be considered as a biosynthetic precursor of 2.
The high diversity of metabolites found in the Amazonian Renealmia nicolaioides strongly recommends further investigation into the chemical and biological properties of the species.

Figure 1 -
Figure 1 -Structures of compounds isolated from rhizomes of R. nicolaioides.

Table I
Pesquisa do estado do Rio de Janeiro (FAPeRJ) for their financial support, and Herison Medeiros and staff of Herbarium of the Universidade Federal do Acre (UFACPZ) for logistical and technical support.This study was part of the PhD of the first author in the Programa de Pós-Graduação em Biociências e Biotecnologia of the Universidade estadual do Norte Fluminense Darcy Ribeiro (UeNF).

TABLE I 1 H and 13 C NMR data of diarylheptanoid 3 in D 3 COD (500MHz) and CDCl 3 (600 MHz).
*From the observed signs with two solvents.