Extract-Only Compounds

[kwetzalkoatl]

Are there any compounds that we can't synthesize, or that are grossly inefficient to synthesize using normal means?

 

Given access to high technology, and plentiful resources, are there any compounds that would still need to be extracted, and could not be synthesized?

 

Please speculate about the characteristics of such compounds. That is, what makes a compound hard to synthesize?

[hypervalent_iodine]

This sounds suspiciously homework-like.

[kwetzalkoatl]

It's for a piece of fiction I'm trying to write. I want to have a scientist growing plants in space, but need a compelling economic reason for him to grow said plants in the first place.

 

On a side note, does your post indicate that homework questions not allowed here?

[hypervalent_iodine]

No, not at all. We welcome homework questions, but we don't welcome people coming in to get others to do their work for them.

To answer your question, there are many, many natural products that remain to be synthesized; either because no one's gotten around to it yet or because they have proven quite difficult to tackle. In these cases, bioharvesting is the only means of obtaining the compound, but this can often be coupled with extremely low yields (in some cases you're lucky to get a few mg from kilos of raw material). On the flip side, there are also a lot of compounds for which bioharvesting is a more economical choice over synthetic means.

Compounds that present the most difficulty in synthesis could broadly be described as those being especially dense in terms of their structure and their functional groups. Polycyclic alkaloids are a good example of this (e.g. the hetisines). The exact reasons for why a certain compound is difficult to synthesise is unique to each molecule, though many of them share common characteristics:

• The are almost always large molecules with a great deal of steric bulk.
• Involves complex and often polycyclic structures.
• Quaternary carbons everywhere.
• Multiple functional groups.
• Heterocyclic structures are common.

(I may have missed something, but you get the idea.)

 

The complexity of these compounds means that a great many present synthetic challenges too difficult to overcome with existing chemistry or require lengthy and expensive (and sometimes quite difficult) protocol to make for an incredibly small return (from start to finish, a 'good' yield of some natural products sits well below 1%). Since one of the largest driving forces behind natural product synthesis is medicinal and agricultural application, you can appreciate why this is quite problematic and how it leads to the necessity to obtain the products from their natural sources. Taxol is probably the best example of this.

 

What exactly do you mean by plentiful resources? Unfortunately, and increase in the quality of technology available might not do terribly much to resolve issues inherent within the chemistry of a given compound, though it may give clues as to ways around them. Technological improvements and developments certainly could make (and has made in the past) some processes more streamlined and affordable on laboratory and industrial scales.

 

Hope that answers your questions.

 

Edit: I should say that one thing improved technology has done in the past few decades is make purification and separation of enantiomers and the like much easier. For some compounds, particularly amines, purification can be nightmarish using conventional means. Automated methods of separation (HPLC, etc.) allow for you to do all sorts of neat tricks that you couldn't do or couldn't do easily otherwise.

[John Cuthber]

I think the most obvious answer would be food.

However there are some drugs that are produced by growing plants.Digitalis, morphine, and taxine are some of them. (From foxgloves, poppies and yew trees)

[kwetzalkoatl]

Many thanks, these are just the sort of considerations i was looking for!

 

Although science fiction is my aim at this point, i certainly don't mean turn a blind to the scientific aspects of my ideas.

 

Maybe I'll even go back for a 2nd term of Organic Chemistry someday...

[Enthalpy]

One common example is natural rubber. It's just poly-isoprene, chemistry knows to make poly-isoprene, but Nature does it better (see Wiki) and on a huge scale. Natural rubber bounces better than artificial one. We still use some in car tyres.

 

A general case is chiral compounds. Biology produces them efficiently, often at 100% left-handed or 100% right-handed, while chemistry tends to make 50-50% mixtures because the enantiomers have the same properties. Drugs are difficult to make partly because only one enantiomer is desired.

 

Also think of extremely cheap materials: petrol, sugar, wheat, ethanol, glass, concrete... We can grow, exploit or transform these for little money, and more elaborate processes can't compete. Here new organic compounds will more likely result from genetic engineering than chemistry.