varoi [104] and from Ambrosia artemisioides [105]. 1,4-Epoxycadinane is a constituent of Dilophus fasciola [106, 107]. Isomaneonene A has been found in extracts
of Laurencia nidifica [97]. Shonachalin B is an example of eudesmanolide isolated
from the aerial parts of Artemisia caerulescens [108] (Fig. 7).
3.4 Diterpenoid 7-Oxabicyclo[2.2.1]heptanes
and Prostaglandin Analogues
The bicyclic diterpene dactylomelol has been isolated from the shell-less mollusc
Aplysia dactylomela [109]. Teupestalin B is a constituent of Teucrium pestalozzae
[110]. 1,4-Epoxy-13-dolastene (Fig. 8) has been isolated from a Dictyota sp. brown
alga [111].
The adversary relationship between prostacyclin (PGI 2 ) and thromboxane-A 2
(TXA 2 ), which modulates coronary blood vessel caliber [112] and platelet aggregation [113], presents opportunities for therapeutic intervention in cardiovascular
diseases. Substances that inhibit TXA 2 synthetase or interfere at the TXA 2 receptor
Fig. 7 Examples of natural polycyclic 7-oxanornornane derivatives
AIBN: Me 2 C(CN)-N=N-C(CN)Me 2
TBS: Si(t-Bu)Me 2
O
OTBS
H
O
O
O
OTBS
SO 2 Ph
H
O
O
OTBS
PhSO 2
H
O
O
OTBS
PhSO 2
H
SnBu 3
ClCH 2 SO 2 Ph
AIBN, PhH, 80
o
C
51
52
53
54
38%
Scheme 7 Renaud and Vionnet’s three-component synthesis of a polysubstituted
7-oxanorbornane derivative
150
A.J. Moreno-Vargas and P. Vogel