IntroductionRed algae is one group of the Protistans according to taxonomic diagram of biomedically interesting organisms. The red algae of the genus Laurencia are known as an abundant source of halogenated sesquiterpenes, diterpenes and acetylenes. Most halogenated sesquiterpenes are found in the algae of the genus Laurencia. Some of halogenated secondary metabolites of the genus Laurencia have been found to be antibacterial, antimalarial, antifungal and antiviral and cytotoxic activities.

ExperimentalIn this study, an extract was obtained by exhausting in chloroform-methanol (1:1) solvent mixture as 14g from L. obtusa, collected from North eastern part of Aegean Sea (Bademli- Ayvalık) in Turkey. Fractionation of the extract on a Si-gel column carried out by the elution starting with petroleum ether, and gradients used first dichloromethane, and then acetone, finally methanol with increasing amounts.

ABSTRACTThe genus Laurencia Lamouroux (Rhodomelaceae) includes about 140 species distributed throughout the world except for the Arctic and Antartic zones[1]. The red algae of the genus Laurencia are known as a rich source of the halogenated sesquiterpenes, diterpenes and acetylenes [2,3]. Although a number studies have been done on L.aurencia obtusa, investigations are still going on this species due to high biodiversity of its constituents. Studies on the secondary metabolites of the alga L. obtusa Lamoroux, which has different colors in different regions of Turkey and at different times afforded over 15 compounds which consist of namely halogenated sesquiterpenes and acetogenins. In a continuation of the studies on L. obtusa, we now obtained two new compounds. Structure elucidation of the isolated pure compounds was done by spectral analyses, including 1D and 2D NMR and mass spectroscopy. Potential bioactivity of the isolates was investigated by following structure elucidation studies.

ResultsSince 1970’s, Laurencia species growing in coasts of Turkey, collected from Aegean sea coasts have been studied by Prof. Dr. Sedat Imre et al. and obtained over a dozen secondary metabolites including namely halogenated sesquiterpenes and acetylenic compounds. Most of their structures are given in Table 1 [4-10]. In the course of our continuing research on the alga Laurencia obtusa, two new compounds were now isolated and their structures were established by intensive NMR and mass spectroscopy, including NOE, HMQC and HMBC experiments. The extract and the pure compounds were analysed for their potential bioactivity including anti-cholinesterase and anti-oxidant activity tests for the new isolates and the extract. Interestingly, each time, even Plants collected from the same location (Bademli-Ayvalik) afforded different compounds although the same extraction procedure was followed. In this study, we have isolated aromatic structures rather than cyclics (Figs 1 and 2).

L.O.1= The other new compound L.O.2= Laurenobtusenene

L.O.3= The Extract(PE) L.O.4= The Extract(MeOH)

Table 1. The Structures of some Compounds of Laurencia Obtusa

Br

OR R=H α- synderol[4] R=Ac α- synderol acetat[4]

Br

Br

OH (8R*)- 8 Bromo-10-epi-β-synderol[4]

Br

Br

OH (8S*)- 8 Bromo-10-epi-β-synderol[4]

O

H BrH

H

Br

O

HH

C15 Acetogenin[5]

O

OH

Br

Br

Obtusenol[5]

O

O

H

HBr

Cl

3-E dactomelyne[5]

OH

OH

OH

Cl

A new sesquiterpene[5]

OBr

R

O

H

H3C

Cl

CBr

R=Br 10-Bromo obtusallene[6] R=H Obtusallene [6]

O

OHOH

H H

HO

OH3CC

Br Kasallene[7]

O

HBr

AcO

Cl

Cl

H

13_epilaurencienyne(3E)[8]

O

H

Cl

BrH

Obtusynenyne[9]

O

OCl

Br Epoxy-trans-isodihydrorhodophytin[10]

C δC δH δH HMBC 1 152.9(Cq) - 6.98 137.2, 152.9, 44.7 2 115.7(CH) 6.53(bds,J=0.78) 6.62 127.4, 115.7, 20.6 3 137.2(Cq) - 6.53 120.6, 20.6, 127.4 4 120.6(CH) 6.62(dd,J=7.81, 0.8) 1.5 127.4 5 124.8(CH) 6.98(d, J=7.81) 1.66

1.89 44.7, 20.6, 127.4, 37.3 -

6 127.4(Cq) - 1.78 2.05

42.3 -

7 44.7(Cq) - 1.1 59.5, 38.1, 31.2 8 85.1(Cq) - 1.40 85.1, 37.3, 59.5, 46.6, 38.1,

31.2 9 46.6(CH) 1.5(dd,J=7.03, 13.67) 2.25 120.6, 115.7, 137.2 10 38.1(Cq) 1.34 44.7, 127.4, 42.3, 46.6

11 42.3(CH2) 1.66(ddd, J=7.3,11.7, 11.7)

1.89(ddd,J=2.3, 11.7, 14.06) 0.79 44.7, 85.1, 46.6

12 37.3(CH2) 1.78(ddd,J=2.4, 11.7,14.06) 2.05(ddd, J=2.3, 7.42, 7.42)

13 59.5(Cq) - 14 31.2(CH3) 1.1(s) 15 23.1(CH3) 1.40(s) 16 7.47(CH3) 0.79(d,J=3.51, 3.51) 17 20.6(CH3) 1.34(s) 18 21.0(CH3) 2.25(s)

Table 2. 13 C NMR(100MHz),1H NMR(400MHz) and HMBC data for Laurenobtusenen(1)

Figure 1. New Compound Laurenobtusenene

O

Br

12

3

4 5

67

9

8 10

11

12

13 14

1516

17

18

Figure 2. The other new compound

Br

O

Cl

Br

-20,00-10,000,0010,0020,0030,0040,0050,0060,0070,0080,0090,00100,00

L.0.1 L.0.2 L.O.3 L.O.4 BHT BHA α-TOC

Antio

xida

nt A

ctiv

ity

(%İn

hibi

tion)

10µg/mL25µg/mL50µg/mL100µg/mL

-10,000,0010,0020,0030,0040,0050,0060,0070,0080,0090,00100,00

L.O.1 L.O.2 L.O.3 L.O.4 BHT BHA α-TOC

DPP

H F

ree

Rad

ical

Sc

aven

ging

Cap

acity

(%

İnhi

bitio

n)

10µg/mL

25µg/mL

50µg/mL

100µg/mL

Figure 3. Antioxidant activity and DPPH

[1] Rodriguez, M.C. Gil et al, Bot. Mar.(1992), 35, 227-237. [6] Oztunc, A. et all, Tetrahedron(1991), 47, 2273-2276. [2] Faulkner, D. J. Nat. Prod. Rep.(1999),16, 155-198. [7] Imre, S. et all, Tetrahedron Letters(1991), 32, 4377-4380 [3] Scheuer, P. J. Med. Res. Rev. (1989), 9, 535-545. [8] Imre, S. et all, Pharmazie(1997), 52, 883-885. [4] Topcu, G. et all, J. Nat. Prod.(2003),66, 1505-1508. [9] Kıng, T.J. et all, Tetrahedron Letters(1979), 16, 1453-1454. [5] Imre, S. et all, Nat. Prod. Res.(2004),18, 43-49. [10] Lotter H. et all, J. of Biosciences(1987), 42, 507-509.