Drimane-Type Sesquiterpenes from Polygonum hydropiper Rajia Sultana 1, 2 , Rashadul Hossain 1, 2 , Achyut Adhikari 2 , Zulfiqar Ali 2, 5 , Sammar Yousuf 2 , Muhammad Iqbal Choudhary 2, 3 , Muhammad Yusuff Ali 4 , Muhammad Shahed Zaman 4 1 Department of Chemistry, Chittagong University of Engineering and Technology, Chittagong, Bangladesh 2 H. E. J. Research Institute of Chemistry, International Center for Chemical and Biological Sciences, University of Karachi, Karachi, Pakistan 3 Department of Chemistry, King Saud University, Riyadh, Saudi Arabia 4 Department of Chemistry, University of Rajshahi, Rajshahi, Bangladesh 5 National Center for Natural Products Research, School of Pharmacy, University of Mississippi, University, Mississippi, USA Abstract ! One new drimane-type sesquiterpenoid, 3β-angeloyloxy-7-epi- futronolide (1), and one new natural product, polygonumate (2), along with six known drimane-type sesquiterpenes [dendocar- bin L (3), (+) winterin (4), (+) fuegin (5), changweikangic acid A (6), futronolide (7), and 7-ketoisodrimenin (8)] were isolated from the whole plant of Polygonum hydropiper Linn. Their struc- tures were determined using spectroscopic techniques. Single- crystal X‑ray diffraction study on dendocarbin L (3) and 13 C‑NMR spectroscopic data of (+) winterin (4) are described for the first time. Compound 6 was evaluated for inhibitions of α-chymotryp- sin, acetylcholinesterase, and butyrylcholinesterase enzymes. Key words Polygonum hydropiper · Polygonaceae · 3β‑angeloyloxy‑7‑epi- futronolide · polygonumate · dendocarbin L Supporting information available online at http://www.thieme-connect.de/ejournals/toc/plantamedica The family Polygonaceae comprises about 55 genera and over 1150 species. The genus Polygonum, annual or perennial herbs, consists of about 60 species [1]. Polygonum hydropiper Linn. (syn. Persicaria hydropiper L.), commonly known as water pep- per, is an annual herb used in traditional medicines for the treat- ment of pain, liver enlargement, gastric ulcer, dysentery, loss of appetite, dysmenorrhea, skin diseases, painful carbuncles, can- cer, and as an hemostatic [2,3]. Various classes of compounds, like drimane-type sesquiterpenoids and norsesquiterpenoids [4–7], flavonoids [8, 9], isocoumarins [10], coumaryl glycosides [11], and phenylpropanoide esters [12] have been reported from this plant. Chymotrypsin enzymes catalyze the hydrolysis of pep- tide bonds involving L-isomers of tyrosine, phenylalanine, and tryptophan. Cholinesterase enzymes catalyze the hydrolysis of neurotransmitter acetylcholine into choline and acetic acid, a re- action necessary to allow a cholinergic neuron to its resting state. As part of our program to search for α-chymotrypsin and cholin- esterase enzyme inhibitors from medicinal plants, P. hydropiper was investigated. Consequently, a novel prenylated sesquiter- pene lactone (3β-angeloyloxy-7-epifutronolide) (1) and a new natural sesquiterpene lactone (polygonumate) (2), along with six known drimane-type sesquiterpenes [dendocarbin L (3), (+) winterin (4), (+) fuegin (5), changweikangic acid A (6), futrono- lide (7), and 7-ketoisodrimenin (8)] were isolated from the CH 2 Cl 2 soluble part of the MeOH extract of this plant. Also struc- ture elucidation was performed using NMR and HR‑TOF‑ESI‑MS spectroscopic techniques (l " Fig. 1). Twenty resonances in 13 C‑NMR spectrum and the pseudomolec- ular ion [M + H] + at m/z 349.2008 (calcd. 349.2015 for C 20 H 28 O 5 + H) in the HR‑TOF‑ESI‑MS of 1 supported the molecular formula of C 20 H 28 O 5 . The IR spectrum showed absorptions for an α,β-un- saturated ester-carbonyl moiety (1693 cm -1 ) and a five-mem- bered lactone with a double bond in conjugation with the oxo group (1743 cm -1 ). The 13 C‑NMR resonances were identified by DEPT experiment as five methyl, four methylene, four methine, and seven quaternary carbons. The 1 H- 1 H COSY, HSQC, and HMBC spectra (l " Fig. 2) were employed to assign NMR spectroscopic data of 1 (l " Table 1). The 1 H- and 13 C‑NMR spectra displayed res- onances in the downfield region for two double bonds [δ H /δ C 6.05 (qq, J 3′,4′ = 7.0 Hz, J 3′,5′ = 1.5 Hz)/137.9 (CH-3′), δ C 128.2 (C-2′), 155.2 (C-8), and 134.2 (C-9)], two ester carbonyl carbons [δ C 172.0 (C-11) and 167.6 (C-1′)], two oxygenated methines [δ H /δ C 4.55 (dd, J 3,2a = 11.5 Hz, J 3,2e = 5.5 Hz)/79.8 (CH-3) and 4.71 (br. t, J 7,6 = 4.5 Hz)/65.0 (CH-7)], and an isolated oxymethylene [δ H /δ C 4.60, 4.64 (each d, J 12a,12b = 17.5 Hz)/70.7 (CH 2 -12)]. Four tertiary methyl and one secondary methyl groups were observed in the up-field region at δ H /δ C 1.02 (s)/28.4 (CH 3 -13), 1.29 (s)/18.5 (CH 3 -14), 1.53 (s)/20.5 (CH 3 -15), 1.97 (d, J 4′,3′ = 7.0 Hz)/15.4 (CH 3 -4′), and 1.89 (d, J 5′,3′ = 1.5 Hz)/20.6 (CH 3 -5′). When the 13 C‑NMR chemical shifts were compared with those of 7-epifu- tronolide [13], the resonance for a methylene (CH 2 -3) was absent in 1. Instead it showed an oxymethine at δ C 79.8 (CH-3) with res- onances for an angeloyl unit [δ C 167.6 (C-1′), 128.2 (C-2′), 137.9 (C-3′), 20.6 (C-5′), and 15.8 (C-4′)] [14]. Angeloyl moiety was placed at C-3 on the basis of the HMBC correlation of H-3 (δ H 4.55) with C-1′ (δ C 167.6), while oxygen atoms at C-3 and C-7 were inferred from interactions of H 3 -13 and H 3 -14 with C-3; H- 3 with C-4, C-13, and C-14; and H-7 with C-5,C-6,C-8, C-9, and C- 12 (l " Fig. 2). Five-membered lactone moiety (C-12 – C-8 – C-9 – C- 11 – O –) was deduced from cross-peaks between H-7/C-8, C-9, C- 12; H 2 -12/C-7, C-8, C-9, C-11; and H 3 -15/C-9 in the HMBC spec- trum. The coupling constants of H-3 signal (J 3,2a = 11.5 Hz, J 3,2e = 5.5 Hz) were characteristic of an axial orientation, and an equato- rially oriented oxygen function at C-3 was deduced. The α-orien- tation of H-3 was supported from its interaction with biogeneti- cally α-orientated H-5, which sequentially interacted with H-7 in the NOESY spectrum and eventually indicated a β-oriented hy- droxy group at C-7. Ultimately, the structure of 1 was elucidated as 3β-angeloyloxy-7-epifutronolide. Compound 2 was obtained as a gummy substance, showing ab- sorption of a five-membered lactone with a double bond adjacent to the oxo group in the IR spectrum at 1748 cm -1 . The molecular formula of 2 was determined as C 16 H 22 O 4 through an [M + NH 4 ] + ion at m/z 296.1862 in the HR‑TOF‑ESI‑MS (calcd. 296.1889 for C 16 H 22 O 4 + NH 4 ). The 1 H- 1 H COSY, HSQC, and HMBC spectra (l " Fig. 2) were used to assign the 1 H- and 13 C‑NMR chemical shifts in 2 (l " Table 1). When the NMR spectroscopic data of 2 were compared with those of 1, resonances for angeloyl unit and two oxygenated methines (CH-3 and CH-7) were absent in 2, but rather showed two methylenes (CH 2 -3 and CH 2 -7). Furthermore, it was also observed that one of the tertiary methyls (CH 3 -14) in 1 1848 Sultana R et al. Drimane-Type Sesquiterpenes from … Planta Med 2011; 77: 1848–1851 Letters Downloaded by: University of Mississippi. Copyrighted material.