Caulerpin from a New Source Spatoglossum asperum: a Brown Alga.

Byline: Jehan Ara, Viqar Sultana, Amna Tariq, Darakhshan Taj, Maria Azam and Viqar Uddin Ahmed

Summary: Caulerpin, an orange-red algal pigment possessing a unique bis-indole structure, has been found in 80% of the species of the green alga genus Caulerpa. Caulerpin and the corresponding diacid have been shown to be plant growth regulators and posses various biological activities. Caulerpin has also been reported from the red alga Chondria armata. This is the first report of the isolation of caulerpin from brown seaweed Spatoglossum asperum J. Ag. The compound was purified by column chromatography and was characterized on the basis of spectroscopic techniques.

Keywords: Caulerpin, Pigment, Isolation, Chromatography, Spectroscopic.

Introduction

Marine algae are potentially luxuriant sources of highly bioactive secondary metabolites that might be useful in the development of new pharmaceutical agents [1]. Alkaloid chemistry is well documented in terrestrial plants, but rare in algae [2].

Caulerpin has been shown to be a plant growth regulator [3] and has been isolated from green algae Caulerpa racemosa and C. peltata [4]. Aguilar-Santos, Doty [5] and Aguilar-Santos [6], reported the isolation of culerpin from green algae Culerpa racemosa, C. setularioides and C. serrulata. Caulerpin was also isolated from other algae: green codium decorticatum [7], Halimeda incrossate [8] and red Laurencia majuscule [9], Hypnea concornis [9], Caloglossa leprieuri [9, 10] and Chondia armata [11].

Studies on Spatoglossum revealed that alginic acid (7.3-15%), crude protein (11-13.4%), iodine (0.06-0.23mg/100g) and ash (10.8-43.2%) were found in Spatoglossum schroederi [12]. Proteinaceous substances which inhibited ethylene formation in apple disks and auxin-induced ethylene biosynthesis by mungbean were isolated [13]. Spatol, a potent inhibitor of cell division, obtained from S. schmittii, was the first metabolite of this series to be described. The potent cytotoxicity of spatol is believed to be associated with the 1, 3-diepoxide moiety in the side chain [14]. S. schmittii also contained the diol and the triol forms while S. howleii produced spatol, diol, triol together with the tetraol and the triacetate [15]. In our studies S. asperum showed cytotoxicity [16] and hypolipidaemic activity [17].

Spatoglossum also improved plant growth [18-20]. We also reported the presence of various fatty acids from S.asperum [21]. The present work describes the isolation, purification and structure elucidation of caulerpin from Spatoglossum asperum. This is the first report on isolation and purification of caulerpin from brown seaweed Spatoglossum asperum.

Experimental

Ethanol extract (20 g) of Spatoglossum asperum J. Ag. was separated into hexane soluble and insoluble portions. The hexane insoluble portion (5 g) was chromatographed on a column of silica gel (70-230 mesh) and was eluted successively with hexane, hexane-chloroform, and chloroform. The fractions eluted with hexane-chloroform (80: 20) afforded orange red crystals. The isolated orange-red crystals were characterized from its m.p. U.V absorption-1NMR, 13C-NMR, IR and high resolution mass spectrum (HRMS).

Results and Discussion

The orange-red pigment has high melting point, 320o C (dec.) and strong UV absorption. Its UV spectrum in methanol showed maximum absorption at I>>max. 221, 269 and 315 and suggested the presence of carbonyl functions in conjugation with the aromatic group (Table1). The infra red (KBr) exhibited peaks at max. 1680, 1631 and 1613s cm-1 and suggested the presence of carbonyl functions in conjugation with aromatic groups. The strong aromatic character is indicated by the i.r. bands at 3400, 1631, 1613, 1488 and 1440 cm-1 and peaks at 730, 920cm-1. The1H-NMR spectrum (CDCl3 , 300 MHz ) indicated the presence of 18 protons. The signals are at I' 3.8 (6H, s, 2 x OCH3 ), 7.0-7.6 (8H, m, Ar H), 8.04 (2H, s, 2 x =CH-) and 9.1 (2H, s, 2 x NH). The aromatic proton signals at I' 7.6-7.0 and 8.2 suggested the presence of two identically substituted condensed aromatic ring systems.

The mass spectrum showed a molecular ion peak at m/z 398 corresponding to the formula C24H18N2O4. In addition, strong peaks were present at 366 (M+-32 or MeOH), 338 (M+-60 or MeCOOH), 306 (M+-92 or [MeOH + MeCOOH]). Other peaks were visible at m/z 279, 251, 199 and 139. The high resolution mass spectrum (HRMS) indicated the molecular ion peak at m/z 398.11855 corresponding to the molecular formula C24H18N2O4 (calcd. for 398.12676). The other prominent peaks were at m/z 366.08904 (C23H14N2O3 calcd. for 366.10052) and 338.09597 (C22H14N2O2 calcd. for 338.10560) corresponded to the loss of CH3OH and CH3 COOH from the molecular ion peak while the peak at m/z 306.06696 (C21H10N2O calcd. for 306.07936) suggested the loss of 92 mu (C3H8O3). Based on the spectral data, the red pigment Caulerpin isolated from Spatoglossum asperum characterized as Caulerpin (I).

Caulerpin, a dimer of indole-3-acrylic acid, behaves much like the indole auxins [22]. Caulerpin a low toxicity compound [23], belongs to the group of bisindole natural products. It contains eight member ring between two indole rings which are directly incorporated with the carbonyl group.

Caulerpin possess different biological activities for instance antinociceptive and anti-inflammatory activities [24], antitumor activity [25] and as a plant growth regulator [3].

Caulerpin was first isolated from three species: Caulerpa racemosa, var. clavifera, C. sertularioides, and C. serulata collected in the Philippines [5]. The distribution of caulerpin has been studied with more than 30 species of Caulerpa from Florida, Bermuda and Tasmania [22, 26]. The occurrence of two related pigments, mono- and di- carboxylic acid forms of caulerpin has also been reported from an Indian collection of C. racemosa [27]. It has not been reported from any other source than the Caulerpales. It has now been reported from a red alga Chondria armata [11]. This is the first report of caulerpin from brown alga Spatoglossum asperum.

The red compound was identified as caulerpin by comparison of its spectral data (UV, IR and1H-NMR) with literature values [5, 28, 29]. Its 13C-NMR, DEPT and mass spectral data further supported its structure. The carbon chemical shifts with sets of identical carbons as indicated in the structure are in full agreement with reported for caulerpin [11]. The crystal structure of caulerpin has been reported [30].

Table-1: Spectroscopic data of Caulerpin.

###UV###1H-NMR###13C-NMR

###Optical###IR (KBr)

m.p.###(MeOH)###EIMS m/z (rel. int.)###HRMS m/z:###(CDCl3 , 300###(CDCl3, 125

###density###max

###I>>max###MHz)###MHz)

###398.11855 (calcd. for

###398 ([M]+, C24H18N2O4, 97%);###3.8 (6H, s, 2###166.6, 142.7,

###3400, 1680,###C24H18N2O4, 398.12676),

###366 (M+-32 or MeOH; 18%);###x OCH3 ), 7.0-###137.7,132.9,

###1631, 1613,###366.08904 (calcd. for

###[[alpha]] D +###338###7.6 (8H, m, Ar###128.1,125.1,

###203, 221,###1615, 1488,###C23H14N2O3,

320o C###0.03###(M+-60 or MeCOOH, 18%),###H), 8.04 (2H,###123.4, 120.7,

###269 and###1440, 1250,###+###366.10052),

(dec.)###(c,0.08,###306 (M -92 or [MeOH +###, 2 x =CH-)###118,

###315 nm###920, and 730###338.09597(calcd. for

###CHCl3).###MeCOOH], 27%), 279 (77%),###and 9.1 (2H,###12.5,111.5 and

###cm-1###C22H14N2O2, 338.10560)

###251 (14%), 199 (8%) and 139###s, 2 x NH).###52.5.

###306.06696 (calcd. For

###(28%).

###C21H10N2O, 306.079

Conclusion

Caulerpin, a plant growth regulator have been reported from green seaweeds. The current study has revealed the occurrence of caulerpin in brown seaweed.

Acknowledgement

We are thankful to Dr. Aisha Begum, Department of Botany, University of Karachi for the identification of seaweed.

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