Amathamides

There have been reports of alkaloids in bacteria and it is possible that some alkaloids in marine invertebrates are actually made by bacteria that live on the surface of invertebrate (see Walls JT, Blackman AJ, Ritz AD. (1995). Localisation of the amathamide alkaloids in surface bacteria oiAmathia wilsoni Kirkpatrick. Hydwbiologia, 297,163-72). It would appear that the search for alkaloids in microbes has been less extensive than in higher plants. It is reported that alkaloids are much less common in lower plants and gymnosperms than in angiosperms. 

Tyrosine-derived metabolites in this section do not include spiro-cyclohexadienyl-isoxazolines and related compounds (Sect. 3.22.3.3) or bastadins (Sect. 3.22.3.4), but they do include tyrosine-derived alkaloids that were covered in the Alkaloids section in the first survey (1). The prolific bryozoan Amathia convoluta, collected in Tasmania, has yielded amathamide G (1953) (1814), the latest of several amath-amide alkaloids from the genus Amathia (1). A Florida collection of this animal furnished the new convolutamines A-E (1954—1958) (1815), F (1959), and G (1960) (1425), and a Tasmanian sample of this bryozoan afforded convolutamine H (1961) (1319). A study of Amathia convoluta from the North Carolina coast has yielded volutamides A-E (1962-1966) (1816). Volutamides B and C reduce feeding by the pinfish (Lagodon rhomboids) and the urchin (Arbacia punctulata), respectively, and volutamides B and D are toxic toward larvae of the hydroid Eudendrium carneum. The New Zealand Amathia wilsoni contains the six novel amathaspiramides A-F (1967-1972) (1817). 

Walls, J.T., Blackman, A.J., and Ritz, D.A., Distribution of amathamide alkaloids within single colonies of the bryozoan Amathia wilsoni, J. Chem. Ecol., 17, 1871, 1991. 

Two other Amathta species which occur in Tasmania have been found to also contain amathamides. A new member of the series, amathamide G, 69, occurs in A. convoluta while A. pinnata contains amathamide C, 64, which has been previously found in A. wilsoni [31], Amathamide G possesses a fully substituted aromatic ring and its structure was secured, in part, by chemical degradation to yield a known compound. 

The chemistry of A. convoluta collected from other regions of the world has also been described and provides yet another example of geographical variability of secondary metabolites. The possible occurrence of bryostatins in A. convoluta from the Gulf of Mexico, has been previously discussed in Section 2.2.1. Since this investigation was directed towards discovering antineoplastlc constituents, the nonactive amathamides would not have been detected. In another recent examination of A. convoluta for secondary metabolites, a series of P-phenylethylamine related alkaloids has been found [32]. The... 

All of the Amathia brominated amides are presumably biosynthesised from amino acids by similar pathways in the related bryozoans. The amathamides are amides derived formally by reaction of 2-(2,4-dlbromo-5-methoxyphenyl)ethanamlne, 68, with proline followed variously by introduction of a double bond, or methyl, methoxy or bromine substituents. The A. convoluta metabolites 70-74, and 75 from A. alternata are all also derived formally from 2-(2,4-dibromo-5-methoxy-phenyDethanamlne, 68—either by direct amide formation with tyrosine, or by having an additional aminopropyl group which is then... 

Figure 4. Schematic of a section of a colony of A. wilsoni showing two major branches with associated sub-branching. Numbers represent total amathamides as percentage dry weight at each location. Pie charts represent the proportion of the major amathamides at the position indicated by the arrows. (Branch angles are schematic only.)...

The amathamides (Scheme 10), alkaloids from the Tasmanian marine bryozoan Amathia wilsoni, have been investigated as a function of geographical location of the collected material (152). Populations from the same location did not exhibit qualitative variations in alkaloid content. However, collections from different, geographically proximate locations gave widely varying alkaloid patterns (Table 1.). 

Only two collections (1 and 3) had an identical main alkaloid, while collection 4 did not give detectable amounts of the main alkaloids of the other samples. Collection 4 had two different alkaloids, collection 3 three, 2 and 5 four, and 1 five. If the amathamides C, D, E, and F of collection 5 are an optimized result of av. evolutionary strategy for survival, then why does collection 4 only have amanthamide A and B In other words, if the population from sample 4 is capable of producing a main component in 95% yield with only 5% minor compound, why then does the population from collection 1 then elaborate five different metabolites ... 

Scheme 10. Structures of the amathamide alkaloids, amathamide A [1], B [2], C [3], D [4], E [5], and F [6] from the marine bryozoan Amathia wilsoni.

If all specimens from the different locations have the genetic set-up for the production of all amathamides, different parts of the genome are apparently expressed in the geographically different populations. This is the most economic route to deal with varying levels and types of challenges. 

Based on the observations Carroll et al. suggested that might be the cell permeability of charged molecules is responsible for lower biologieal aetivity [43], Biogenetically wilsoniamines A (80) and B (81) might be derived from amathamides. 

OMe O Me 116 Amathamide F (As published in literature) (Revised, Unpublished results)... 

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