A Novel Compound from the Bark of Diospyros lotus and their Urease Inhibitory Activity
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A NOVEL COMPOUND FROM THE BARK OF Diospyros lotus AND THEIR UREASE INHIBITORY ACTIVITY
Abdur Rauf,1* Abdullah S. M. Aljohani,2 Fahad A. Alhumaydhi,3 and Saima Naz4
One novel dimeric naphthoquinone, 1′,4′-dihydroxy-5,8-dimethoxy-11,11′-dimethyl-[7,3′-binaphthalene]1,4,5′,8′-tetraone, was isolated from the chloroform-soluble fraction of Diospyros lotus bark. The chemical structure of compound 1 was elucidated by advanced spectroscopy techniques, such as 1H, 13C NMR, HMBC, HSQC, COSY, and NOSEY. The chloroform extract and compound 1 were evaluated for their urease inhibitory activity, which showed excellent results with IC 50 value of 421.21 and 68.42 μM, respectively, against thiourea (IC 50 = 21.24 μM). Keywords: Diospyros lotus bark, dinaphthodiospyrol, urease inhibition. Diospyros lotus is a member of the family Ebenaceae, which is commonly known as date plum, lilac persimmon, or Caucasian persimmon [1]. It is found in tropical and subtropical southwest Asia as well as in southeast Europe. D. lotus is among the oldest plants in cultivation in various parts of the biosphere [2]. Its fruits are called Amlok and are consumed by humans and animals directly. Its height ranges from 15 to 30 m, while the leave is oval shape, leathery, and shiny; the pointed end size ranges from 5 to15 cm long and 3–6 cm in width. Its flowers are greenish, which grow in June to July. The fruits are yellow, with juicy flesh, and it is the favorite food of jackals [3, 4]. Different parts of D. lotus, including fruits, bark, and leaves, are used in traditional medicine for the treatment of various diseases [3, 5]. The leaves are used for the treatment of lumbago; the fruits treat indigestion, the seeds lower anxiety, while the bark cures fever [2]. This plant is explored very little phytochemicaly. Recently, the isolation of a new series of phytochemicals including dimeric naphthoquinones [6], triterpenoids [7], phenolic compounds [8, 9], and other important phytochemicals [10–12] has been reported. Other traditional usages are as antifungals, antihypertensives, vermicides, and bactericides [4, 6]. The Diospyros genus yields triterpenoids such as betulin, betulinic acid, and ursolic acid, which exhibit anti-inflammatory activity [13]. The compounds previously isolated from the title plant possess strong anti-proliferative, anticancer, sedative, analgesic, and anti-inflammatory activities. Compound 1 was isolated as a red amorphous mass from the chloroform-soluble fraction of D. lotus. It EI-MS showed a molecular ion peak at 434.20 (calcd for C 24H18O8, 434.40) consistent with the molecular formula C 24H18O8. The FT-IR exhibited absorption bands at 3654 for hydroxyl (OH) stretching, at 2990 for CH, at 1660 for a conjugated C=O group, and at 1607 and 1465 cm–1 for the CH aromatic stretch. The UV showed maximum absorption at 259, 291, and 436 nm. The number and type of carbons and protons were identified by 1H and 13C NMR. The 1H NMR showed two tertiary methyls at δ 1.98 (s, H-11) and 1.97 (s, H-11′), every three protons and two methoxyls at
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