Aphid pigments

Giles and coworkers have recently reported the use of TiCU in CH2CI2 at -78°C for the stereoselective isomerization of naphthyl- and phenyl-dioxolanes to yield pyrans that are important in aphid pigments. 13 Other Lewis acids besides TiCl4 such as BF3, SnCU, Ti(IsoPr)2Cl2 and Ti(IsoPr)3Cl are not effective in such reactions. NMR and nuclear Overhauser effect spectroscopies were used to establish stereochemistry. Some diol side product (13 %) was also formed. The major effort in this research was to clearly identify products of the isomerization. 

Dimeric naphtho[2,3-c]pyrans, containing one quinonoid system, constitute molecules of the aphid pigments deoxyprotoaphin, protoaphin fb, and protoaphin si (64JCS51 66JCS(C)1825 72AJC2199 83CC51). 

A major project was the study of aphid pigments, a topic whose origins can be traced to Todd s experience with anthraquinoncs in his Oxford days. The compounds, though quinonoid in character, were much more complicated and only with the advent of NMR were the structures finally solved. A. W. Johnson, S. F. MacDonald, and, later, D. W. Cameron, led an enthusiastic international group, whose work involved not only chemistry but the detection and harvesting of aphid infestations from the broad bean... 

Isochromans result from the intramolecular C-H insertion reactions of contributing singlet and triplet states of 2-(alkoxymethyl)phenylcarbenes (94TL1699). The cyclisation of both the 2-ally 1 and the 2-prop-T-enyl substituted 3-(l-hydroxyethyl)naphthalene derivatives (9), (10) leads stereoselectively to the trans-n htho[2,3-c]pyrans (11), the heterocyclic moiety of some aphid pigments (94JCS(P1)859). The alkylation of 2-acetylnaphtho-... 

Aphid pigments, YIO Aplysin, T12 Aplysinol, T12 Aplysterol, TlS Apoaromadendrene, T26 Apoaromadendrone, T26... 

Jenkins R. L., Loxdale H. D., Brookes C. P., and Dixon A. F. G. (1999). The major carotenoid pigments of the grain aphid, Sitobion avenae (F.) (Hemiptera Aphididae). Physiol Entomol 24 171-178. 

Beta-cartone sits in the aphid s cell membranes like the red molecule in the pink-lake bacteria. It collects light, which (through an unknown mechanism) excites electrons and pushes them onto an NADH-Uke electron box. Then the electrons are used to make ATP. Overall, sunlight hits the carrot pigment, and its energy is turned into ATP for the aphid to live on. Could this aphid be made an honorary plant ... 

The suffixes -fb, -jc, -si and -tt refer to the aphid species from which the relevant pigments are obtained, e.g. -fb pigments from Aphis fabae [7]. 

Figure 7.17 The carotene pigments in the two colour forms o/Macrosiphum liriodendri aphids. The systematic names are used here. p,p-Carotene is more commonly known as -carotene...

The carotenes of one aphid (Macrosiphum liriodendri), that occurs in two colour variants have been studied in detail. This aphid, living on tulip trees Liriodendron tulipifera), exists in green and pink forms which appear to differ in their level of cyclizing enzymes. The green form have all cyclized carotenes, while the pink form have two partly cyclized and two uncyclized carotenes (Figure 7.17). It must be presumed the aphids have the necessary enzymes to cyclize lycopene. Many other insects, particularly aphids, contain carotenes along with other pigments. 

Aphids make their own pigments, called aphins, not found in any other insects. Their complex chemistry was studied by Lord Todd in the 1950s and 60s. Aphins are dimeric naphthoquinones. The two most important are protoaphin-y (isolated first from the common bean aphid Aphis... 

Figure 8.17 The formation of the aphins, pigments of aphids. The naphthalene derivative first formed is converted into quinone A and glucoside B, which linked together give the aphins. Note that aphinin-ib and aphinin-sl differ by only one chiral centre. There is restricted rotation about the central bond. Structure a shows the twist in the molecule with the right side of the upper portion turned toward the reader and the right side of the lower portion turned away. The structural study of aphinin-Po has never been completed...

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