New polyacetylenes from the sponge Siphonochalina sp.

Six new compounds, characterized by a long unsaturated alkyl chain (nC₂₂), were isolated from a marine sponge. All compounds except for one, possess an enyne terminus on one side of the molecule and either a terminal acetylene (in four) or a propargyl alcohol on the other end. Four of the compounds were unequivocally identified mainly by spectroscopic methods. Acetylenic compounds are well-known constituents of plants: only few, however, are known from marine organisms and to our knowledge only one group of compounds contains more than a single triple bond. Among the acetylene containing marine natural products are: A group of halogenated ethers, characterized by a straight-chain C-15 carbon skeleton and a terminal enyne function which has been isolated from algae¹ and a sea hare², carotenoids³, two steroids⁴, a sesquiterpene⁵ and polyketids^6,7. A diacetylene was found in a group of several n C-22 straight-chain compounds isolated from a marine sponge⁸. One of the compounds found in the latter sponge contains, again, the enyne terminus - an end group which turns out to be quite abundant in the above and the herewith discussed compounds. In our continuing search for bioactive compounds from marine organisms we have isolated from the sponge Siphonochalina sp.⁹ collected at several places in the southern part of the Gulf of Eilat (the Red Sea) six n C-22 straight-chain acetylenic compounds. Extraction of the freeze-dryed sponge (petrol ether, 4% dry weight) and subsequent repeated chromatographies (LH-20 and Silica gel)^10,11 gave six closely related new compounds, named in order of polarity, Δ¹⁵-docos-1-yne (1; RF^12a=0.65; 0.2% based on the dry weight of the animal), octahydrosiphonochalyne (2; Rf^12a=0.55; 0.4%), dihydrosiphonochalyne (4; Rf^12a=0.44; 0.1%) siphonochalyne (3; Rf^12b=0.34; 0.2%), dehydrosiphonochalynol (6; Rf^12b=0.55; 0.1%) and siphonochalynol (5; Rf^12b=0.43; 0.3%).