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I was doing research on buckwheat sprouts (as to whether I should include them in my diet) and I came across a website that said eating too much can cause fagopyrism, which is caused by compounds called fagopyrins:

enter image description here

I was just wondering how they came to the conclusion that it was these compounds that were dangerous? If someone reports side effects, with the number of different chemical compounds in a plant, how would they narrow it down to that one?

Do they just toxicity test all of the possible compounds? Or do they look for certain functional groups and structures to narrow down their search? Ie is there a way you can predict from the structure that a compound could be potentially toxic?

Thanks!

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    $\begingroup$ I changed your title as that seems to be the real basis of your question. Your train of thought is good, but by the end of it you have quite a different question, which can have quite a different answer: it goes from "how do you know which component is toxic" to "how to you predict toxicity from the structure". $\endgroup$
    – orthocresol ♦
    Jan 19, 2021 at 13:00
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    $\begingroup$ Drinking too much water would kill you(like the man advertising drinking many litres daily.). Does it mean drinking water is dangerous ? It is not. Drinking/eating too much of anything would cause some problems or others. Only the dose and circumstances decides if it is a poison. E.g. drinking of infusion of Hypericum perforatum is generally very healthy. But hypericine may kill you if combined with excessive sunbathing, what was abused in ancient Rome. Fagopyrism is similar case. $\endgroup$
    – Poutnik
    Jan 19, 2021 at 14:22
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    $\begingroup$ Fagopyrin is located almost exclusively in the cotyledons of the buckwheat herb. When ingested, fagopyrins cause sensitivity to light. $\endgroup$
    – Poutnik
    Jan 19, 2021 at 15:02
  • $\begingroup$ All what you suggest is in part true. I do not think you are asking about technical procedures like analysis isolation etc but rather on how to assess which compound is toxic. Ubiquitous or largely diffused molecule can be let apart. Then one focus on the characteristic ones. Plus unfortunately comes experimenting... $\endgroup$
    – Alchimista
    Jan 20, 2021 at 11:01

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You have many questions nested together. Whenever you have a mixture + identification of components in your mind, bring chromatography to your mind. You must be familiar with paper chromatography. Same idea, but applied to more sophisticated instruments.

When you have a completely unknown mixture, you start a so-called screening procedure with a high-performance liquid chromatograph and a mass spectrometer. The HPLC separates the components, and the mass spectrometer identifies the molecules from the fragmentation pattern and molecular mass.

You start to see how many components are there in the HPLC-MS chromatogram. Let us say you had natural products and you see 100 peaks (which is not unusual at all).

Later you scale up the process, go at a preparative scale and start collecting fractions of mixtures. You perform biological tests on them, and the relevant fraction is further studied by more advanced tools such as recycling the HPLC-NMR system.

The question you ask is equivalent to a decent Ph.D. project in natural product isolation and characterization followed by investigating their biological activity. In pharmaceutical companies, HPLCs run day and night with a typical HPLC may have 10-15 columns for screening as to which column under which mobile phase will produce the best separation.

I did not check how fagopyrins were discovered, but the process is general. Wiki gave a hint on the first German reference Fagopyrin, ein photodynamischer Farbstoff aus Buchweizen (Fagopyrum esculentum) = Fagopyrin, a photodynamic dye out of buckwheat, locked behind paywall. This procedure is from 1950s, when HPLCs did not exist but the technique of chromatography was very well known.

Wir haben aus einem Methanolextrakt von getrockneten Buchweizenblüten durch fraktionierte Verteilung und chromatographische Adsorption einen photodynamisch wirksamen Farbstoff in Form eines dunkelroten, fast schwarzen mikrokrystallinen Pulvers isoliert, der im folgenden als Fagopyrin bezeichnet ist.

We have isolated from a methanol extract of dried buckwheat flowers by fractional partitioning and chromatographic adsorption a photodynamically active dye in the form of a dark red, almost black microcrystalline powder, hereafter referred to as fagopyrin.

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