About this Author
Derek Lowe, an Arkansan by birth, got his BA from Hendrix College and his PhD in organic chemistry from Duke before spending time in Germany on a Humboldt Fellowship on his post-doc. He's worked for several major pharmaceutical companies since 1989 on drug discovery projects against schizophrenia, Alzheimer's, diabetes, osteoporosis and other diseases.
To contact Derek email him directly: derekb.lowe@gmail.com
Twitter: Dereklowe
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November 2, 2007
Posted by Derek
I was interested to see a recent paper in Organic Letters on a class of compounds I'd never seen before: 1,2-dihydro-1,2-azaborines. There's the structure, in case that doesn't immediately call something to mind.
These things, which are isoelectronic with benzene, were made by the Liu group at Oregon. Their method (ring-closing metathesis) for making them seems superior to the rather sparse techniques that have been available up until now, and they've prepared a number of useful and interesting intermediates. They're rather stable - even the B-H compound with an N-ethyl group, the simplest in the paper, can be run down a silica gel column. An X-ray structure shows that the ring is indeed flat, and it seems to be aromatic and delocalized.
So. . .what I'd like to know is, who's going to be the first person wild-eyed enough to put this in a drug candidate structure? Boron has a bad reputation ("boron for morons", as they say), but hey, Millennium is out there making money with Velcade, a boronic acid. I have absolutely no idea what the fate of this heterocycle is in vivo, what its toxicity might be or what it gets metabolized to (if anything). And neither do you, nor does anyone. Let's find out!
Comments (11)
+ TrackBacks (0) | Category: Chemical News | Odd Elements in Drugs
September 17, 2007
Posted by Derek
As I was mentioning the other day, the latest issue of Nature Medicine has the details on a story that doesn’t, on the face of it, do the industry any credit. About twenty years ago, there were reports out of China that a solublized form of arsenic was very effective in treating acute promyelocytic leukemia, a rare (and fatal) form of the disease. Arsenic had been used as a folk remedy for such conditions, as it has been for many others (often with much less justification!), but its most common compounds (like arsenic trioxide) are tremendously insoluble. The Chinese authors had found a way to make that one go into solution where it could be dosed, but didn’t disclose it in their publication.
That left the door open to someone else, namely a small company called PolaRx. They found a way to do the same thing with the oxide (as far as anyone can tell), and got a patent on its use in oncology. Over years, mergers, and reshuffles, the patent finally ended up in the hands of Cephalon, who now market the soluble arsenic trioxide. However, a course of treatment costs about $50,000, which means that for many patients around the world, the drug is totally out of reach.
Even across the entire world, there aren’t that many patients for this therapy, so the price would tend to be high no matter what. It’s worth remembering that production costs are not a major factor in the pricing of most drugs. We’re not indifferent in this business to how much it costs us to make something, far from it, but we try to keep that a small part of the price. So what does set the price? What sets the price is what sets most prices in this world: what the market will bear. A drug that only treats a small number of patients every year is going to cost a lot of money, no matter what it’s made out of. A company will not market a compound unless they can use its profits to help defray the costs of all the things that don’t make it to market at all.
Cephalon is charging what their market will bear, which is their right, but their market is the health insurance organizations of the industrialized world. That’s another thing to remember – drug companies aren’t selling direct to patients most of the time. They’re selling to insurance companies, and first-world health insurance will put up with a lot of things that no one else can or will. There’s a lot of room to talk (and to complain) about this (I think it distorts pricing signals something fierce), but all the complaints have to start with the realization that this is how things are now set up. Cephalon, for its part, says that it’s open to compassionate use of its drug – that is, providing it to people in need who absolutely cannot afford it. With any luck articles like the Nature Medicine one will help to get the word out about that, and we’ll see how well they follow through.
It’s tempting to blame the patent system for this whole situation – after all, the only reason the company can charge these prices is that they’re the only ones who can sell it, right? But perversely, this might actually show the need for more use of patents rather than less. As another piece in Nature has helpfully reminded people, patents not only grant a period of exclusivity. In return for that, you have to tell people how to replicate your invention.
The alternative, in countries that don’t follow this system, is usually secrecy, and I can’t help but think that this is why the original Chinese work didn’t disclose all the details. A strong patent system eliminates a lot of trade-secret grey areas: someone owns a discovery (for a predetermined period of time), no one owns it, or everyone owns it. There’s none of this “someone owns it until someone else finds out about it” stuff.
But my guess is that the Chinese lab, being used to a trade-secret (or government-secret) culture, reflexively held back their important details. If they wanted to make sure that no one could patent anything, they would have (or at least should have) put all the information out into the public domain, where it would have been prior art against anyone attempting to file on it. (But see below - would that have helped get it through clinical trials, or not?) It’s worth noting that if a patent had been filed back in the early 1990s, the drug would not only have come to the world’s markets faster, the patent would also be much closer to expiration by now, opening up its production. The US researcher who formed PolaRx and filed the patent, Raymond Warrell (now chairman of Genta), stands up for it in the Nature Medicine article, and like it or not, he has a point, too, saying that the patent stimulated interest in the compound: "Without the patent, it would have remained a curious Chinese drug, not available to anyone else." I should note that there may well be room to argue about the validity of the patent, from prior-art concerns, but no one (as far as I know) has seen fit to challenge it.
But I can say for sure that without intellectual property protection in the US and Europe, no drug company would have touched the compound. Without industrial input, the drug would have either never reached the market at all (arsenic trials were a hard sell at the FDA), or would have likely come on more slowly. (That ticking patent clock does keep an organization moving, I can tell you). And now its success in the market has other companies working on improved versions of the therapy. This is how our world works, and (for better or worse) there's no requirement that it be aesthetically appealing.
Comments (8)
+ TrackBacks (0) | Category: Cancer | Drug Development | Odd Elements in Drugs | Patents and IP | Why Everyone Loves Us
January 8, 2006
Posted by Derek
Some time ago I wrote about some atoms that I wish I could use. There are still other molecular fragments that Nature has neglected to provide, though, and I'm adding to the wish list:
First off, I'd like some groups that are plain linear spacers of different lengths. Ideally, we could stick these onto carbons and heteroatoms alike. As it stands, the only commonly available group that does this is an alkyne (a carbon-carbon triple bond), and those come with their own baggage. While there are drugs that have these groups in them, they're typically treated pretty roughly by the liver enzymes. A metabolically stable alkynish thing, of variable length, would be a wonderful thing. People have made various weirdo spacers out of small bicyclic systems, true, but the synthetic routes to them are beastly, with no improvement in sight. Until we can source these things by the kilo, drug companies aren't going to be interested.
Next, I'd like some six-membered heteroaromatic rings with something other than nitrogen in them. As it is, pyridines, pyrimidines, and pyrazines are given a real workout in drug discovery programs, and we'd love to have some more options. Unfortunately, the fabric of the universe hasn't accomodated us. If you put an oxygen in there instead, it has to take on a positive charge, and that gives you a highly reactive beast called a pyrylium. It's rare that you can get one of those into a bottle, and even if you did, sending one in for biological testing would be grounds for a referral to the HR department. I see that some zanies have tried, though.
Sulfur can do the same lively thing, although I've never actually seen any of those, and there's probably a good reason for that. Varioius sorts of aromatic rings with a phosphorus atom in them are known, but they're cranky and exotic, like a lot of phosphorus chemistry. Actually, a lot of phosphorus chemists are kind of that way, too, in my experience. Like a lot of phosphorus compounds, those aryls probably reek to the skies, too. As for phosphorus chemists reeking, I'd say my personal data set runs about fifty-fifty.
And finally, I'd also like some big, lumpy polar atoms. As it is, if you want to put a single lunker of an atom onto a molecule, you're looking at a bromine substitution. Iodine's possible and even larger, but those compounds are usually too unstable to sunlight to make good drugs, unless you're doing thyroid receptor ligands, where you might have to have them whether you feel like it or not. It's true that a trifluoromethyl group is kind of like a big halogen atom, too. But all these halogens make your molecule rather greasy, which is something we'd rather avoid. Something the size of a bromine that could hydrogen-bond and help its molecule go into aqueous solution would be a big hit. Quantum mechanics, being perverse, has not obliged.
Comments (5)
+ TrackBacks (0) | Category: Odd Elements in Drugs
May 2, 2004
Posted by Derek
Another chemical element that you don't see much in pharmaceuticals is silicon. Hey, it's right under carbon in the periodic table, and forms four tetrahedral bonds just like carbon does, so why not, eh?
Now, if you're like me, you grew up reading old science fiction stories that posited silicon-based life forms. That seemed pretty plausible to me when I was a kid, and rather a long shot as I got older, but learning chemistry for real made me realize just how unlikely that is. For one thing, silicon-silicon bonds get progressively weaker as you try to make longer and longer chains, as opposed to carbon chains, where there's no real effect. Silicon's more unstable to oxidation than carbon is, too. If you open up a tank of methane, it'll just hiss all over the room. But if you open up a tank of silane, you'd better have the fire department on the line already.
And silicon doesn't form double bonds very well at all, not with itself or carbon (which means, practically speaking, no alkenes and no aromatic rings) or even with oxygen (which means no analogs of amides, for one big thing.) It gives you a new appreciation for carbon, it does.
Your nose can tell that there's something off about the element. It isn't fooled by its position in the periodic table. Many organosilanes have a distinctive, hard-to-describe smell, a sort of flat, spicy, camphor-like reek, and this smell persists over a fairly wide range of structures that normally would be enough to mask it.
But sulfur smells like Satan's socks, and it's vital. There's no problem with working some single-bonded silicon into your molecules, at least on paper. Reasonable organosilanes are stable to normal sorts of things, and there's no particulary toxicity associated with the element. When I was doing my post-doc in Germany, I even saw ads for silicon-containing supplements, which claimed that it was vital for health. That's pushing it, to say the least, but at least it's not vital for sickness.
There sure aren't many examples, though. I'm virtually certain that no human drug has ever been marketed with a silicon atom in it. DuPont actually took a fungicide to market with one, but pharmaceutical chemists look a bit askance at what the crop science folks can get away with. (Where's the challenge, we keep thinking a bit unfairly, in dosing something that doesn't have a gut or a liver?)
There was a cholinesterase inhibitor in development a few years ago with a silicon, and recently there have been some reports of organosilane-based protease inhibitors. A few other such one-offs show up in the literature. From the scattered reports, you can tell that folks have every so often worked up the nerve to take one into the clinic, but nothing's made it all the way through. That keeps many teams from making a big effort, frankly. Who wants to be the first to find out that there's a problem with, say, liver enzymes after ten years of dosing? Most companies would rather let someone else turn over that card.
I've made a silicon analog or two myself over the years, and reaction from my colleagues and supervisors has been, well, mixed. Some fans of the weird cheered the compounds on when they saw them, while other people rolled their eyes almost audibly. None of the compounds were active enough to force any issues, though.
But one small English company is trying to break the silaceous ice, targeting silicon compounds for pharmaceutical use specifically because they believe they've been underexplored. Good look to Amedis of Cambridge, I say. Perhaps they can make the element respectable.
Comments (3)
+ TrackBacks (0) | Category: Drug Development | Odd Elements in Drugs
April 19, 2004
Posted by Derek
I had a question recently about why some chemical elements don't appear much in pharmaceuticals. Boron was one example - the first boron-containing drug (Velcade, from Millennium) was approved just recently.
But it hasn't been for lack of trying. Starting in the 1980s, several drug companies took a crack at boronic acids as head groups for protease inhibitors. Big, long, expensive programs against enzymes like elastase and thrombin went on year after year, but no one could get the things to quite work well enough. In vitro they ruled - a good boronic acid is about as good as an enzyme inhibitor can be. But in vivo they had their problems, with oral absorption and cell penetration leading the way.
As far as I'm aware, there's no particular tox liability for boron. Things like boric acid certainly don't have a reputation for trouble, and we don't take any special precautions with the air-stable boron compounds in the lab. It'll be hard to make any case, one way one another, based on the Velcade data, since the drug's mechanism of action (proteosome inhibition) has a lot of intrinsic toxicity anyway. (There's the anticancer field for you - there aren't many other areas where a target like that would even be considered.)
I think self-censorship is why there aren't more boron-containing structures out there. We don't spend much time looking at the compounds seriously, because everyone knows the problems with boronic acids, and no one wants to be the first to develop a different boron-containing functional group, either. "Why be the first to find a new kind of trouble?", goes the thinking. "Don't we have enough to worry about already?"
Comments (4)
+ TrackBacks (0) | Category: Odd Elements in Drugs | Toxicology
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