1. Introduction
Red 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.
Experimental
In 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.
ABSTRACT
The 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.
Results
Since 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
R=H α- synderol[4]
R=Ac α- synderol acetat[4]
(8R*)- 8 Bromo-10-epi-β-
synderol[4]
(8S*)- 8 Bromo-10-epi-β-
synderol[4]
C15 Acetogenin[5] Obtusenol[5] 3-E dactomelyne[5]
A new sesquiterpene[5]
R=Br 10-Bromo obtusallene[6]
R=H Obtusallene [6] Kasallene[7]
13_epilaurencienyne(3E)[8] Obtusynenyne[9] 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),1
H NMR(400MHz) and HMBC data for
Laurenobtusenen(1)
Figure 1. New Compound Laurenobtusenene
Figure 2. The other new compound
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L.0.1 L.0.2 L.O.3 L.O.4 BHT BHA α-TOC
AntioxidantActivity
(%İnhibition)
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mL
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mL
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mL
100µg/
mL
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L.O.1 L.O.2 L.O.3 L.O.4 BHT BHA α-TOC
DPPHFreeRadical
ScavengingCapacity
(%İnhibition)
10µg/m
L
25µg/m
L
50µg/m
L
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.