Endiandra

Polycyclic endriandric acid A-like Endiandra introrsa C.T. White, Lauraceae, Ang. from Australian foests MI). Macrolides ervthromvcin-like erythromycin Streptomyces erythreus, Actinom., Bact. from the Philippine soil and picromycins, from temperate soil MI). 

Diels-Alder reactions have been postulated as key steps in a number of biosynthetic conversions. The biosynthesis of the endiandric acids 26 and 27 is discussed below as an example for a spontaneous [4-i-2]-cyclo-addition. This class of compounds which is produced by the Australian plant Endiandra introsa (Lauraceae) is remarkable, because different constitutional isomers were formed simultaneously and in all cases racemic mixtures were synthesized by the plant. It was first postulated by Black et al. [10] and later confirmed via biomimetic total syntheses by Nicolaou et al. [11] that the endiandric acids A, B and C (26a, 26b and 27) are formed by a cascade of electrocyclic reactions (Scheme... 

Reduction-triggered pericyclic reaction has been used for the biomimetic total synthesis of endiandric acids A-G [72]. Endiandric acids are polycychc natural products isolated from the Australian plant Endiandra introrsa and exist naturally as a racemic mixture which is found to have very high antibacterial effect [73]. In 1980, Black and coworkers [74] proposed a hypothesis that these polycyclic systems are formed in nature by a series of electrocycUzation reactions. On the basis of this hypothesis, Nicolaou et al. [72c] in 1982 reported an excellent domino reduction/electrocyclization process for the synthesis of endiandric acid A 127 (Scheme 9.25). Selective hydrogenation using a Lindlar catalyst of diacetylenic diol 123 afforded the bicyclic diol 126. The reaction presumably proceeds via polyene 124, which then undergoes a spontaneous 8 [i-electrocyclization to give 125. It follows a second 6n-electrocyclization to afford bicyclic 126, which is further converted to endiandric acid A 127. 

Constit. of Endiandra introrsa. Rosettes (EtOH) and (CHCl3/petrol). Mp 163-165°. Racemic. 

Stamens with appendages in the outermost androecial whorl are only present in a few genera of extant Lauraceae Rhodostemonodaphne p.p., Urbanodendron, Phyllostemodaphne, Brassiodendron, Endiandra, Cryptocarya Hyland, 1989 Rohwer, 1993), some Hernandiaceae (Kubitzki, 1970a, b, 1993b), Atherospermataceae (Philipson, 1993), and a fewMonimiaceae Hortonia, Peumus, Monimia] Philipson, 1993). 

Fig. 2. Racemic mixtures of endiandric acids A-C shown to occur in nature as constituents of Endiandra species and expected to arise from achiral precursors in nonenzymatic reactions.

In pursuing the role of the Diels/Alder reaction in the biosynthesis of natural products, the endiandric acids [7] provide the point of the story. Fig. 2 shows the structural formulae of three constituents of Endiandra species. Despite the presence of eight stereogenic centres in each structure, all three acids are optically inactive. They happen to exist as racemic mixtures and were suspected to arise from achiral precursors in a cascade of non-enzymatic reactions. Among those reactions an intramolecular Diels/Alder cycloaddition was thought to take place. K.C. Nicolaou [8] was able to verify the endiandric acid-cascade in the laboratory and to support the existence of the non-enzymatic biosynthetic pathway. 

Endiandra introrsa (Lauraceae) is a large tree growing in northern New South Wales and southern Queensland, Australia. Endiandric acid A (115) was obtained from leaves and leaf stems of this plant in a relatively high yield (0.45%) (2). The structure of this compound was determined as 2-(6 -phenyltetracyclo[5,4,2,0 , Oio,i2] trideca-4, 8 -dien-ir-yl)acetic acid by X-ray crystallographic analysis (2, 5). 

Bandaranayake W M, Banfield J E 1980 Endiandric acid, a novel carboxylic acid from Endiandra introrsa (Lauraceae) X-Ray structure determination. J Chem Soc Chem Commun 162-163... 

Bandaranayake W M, Banfield J E, Black D St C, Fallon G D, Gatehouse B M 1982 Constituents of Endiandra species. III. 4-[( ,E)-5 -Phenylpenta-2, 4 -dien-F-yl]tetracyclo-[5,4,0,0 , 0 ]-undec-lO-ene-8-carboxylic acid from Endiandra introrsa (Lauraceae). Aust J Chem 35 567-579... 

Banfield J E, Black D St C, Fallon G D, Gatehouse B M 1983 Constituents of Endiandra species. 

Finally, it is interesting to speculate that Nature may actually utilize aqueous Diels-Alder chemistry for the biosynthesis of the endiandric acids. These compounds are produced in the leaves of Endiandra introrsa (Lauraceae) - presumably in the vicinity of a largely aqueous cellular medium. The biosynthesis of endiandric acid A (1.10) proposed by Black s group [5] involves two sequential electrocyclization reactions (1.7 1.8- 1.9) followed by an intramolecular Diels-Alder reaction to give... 

The endiandric acids, e.g. (142), are an interesting series of natural products which were isolated recently from leaves of the Australian shrub Endiandra introrsa. They each have eight asymmetric centres, and occur in Nature in racemic rather than enantiomeric forms, which is a rather unusual observation for naturally occurring compounds. 

---