10.12.2012 Views

netLibrary - eBook Summary Structure-based Drug Design by ...

netLibrary - eBook Summary Structure-based Drug Design by ...

netLibrary - eBook Summary Structure-based Drug Design by ...

SHOW MORE
SHOW LESS

You also want an ePaper? Increase the reach of your titles

YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.

Document<br />

Page 509<br />

The correlation of potency with logP might suggest that A rings with the lowest hydrogen-bonding<br />

potential would be the most potent. This has not been shown to be true. In fact, rings with heterocyclic<br />

nitrogen atoms are preferred to furan and thiophene rings, which would be expected to have less<br />

hydrogen-bonding potential [86,87]. This observation even extends to tetrazole rings, which have often<br />

been used in pharmaceutical design to replace hydrophilic groups such as carboxylates or esters.<br />

Explanations for the variability in potency due to A-ring changes have not been satisfactory. These<br />

heterocycles lack any consistent pattern of hydrogen bonds with the pocket residues (Table 6) [88]. Like<br />

QSAR analysis, structural analysis has not been able to show any relationship between hydrogenbonding<br />

groups in the A ring, or dipole moment, and potency [80,85].<br />

Extensive structural characterization of many different A-ring heterocycles has not yet been done.<br />

Difficulties predicting relative potency of these compounds a priori stem from the lack of understanding<br />

of solvation/desolvation effects as well as difficulties in characterizing the low-intensity hydrophobic<br />

interactions. Consequently, it seems likely that new structure—activity relationships about the A-ring<br />

heterocycle will continue to be determined <strong>based</strong> on empirical findings.<br />

Hydrogen-Bonding Requirements<br />

Capsid-binding compounds with a hydrogen-bond accepting atom in the region of the drug that binds to<br />

the VP1 pocket heel appear to demonstrate greater potency than do their non-hydrogen-bonding<br />

counterparts (Table 7) [55,89]. Studies using HRV14 where Asn1219, a hydrogen-bond donor in the<br />

pore region, has been mutated to Ala have shown that the compounds bind as well in the mutated virus<br />

as in the native virus [27]. This might suggest that the hydrogen bonding to Asn1219 at the pocket pore<br />

is unimportant. Recent structures of compounds in HRV14 have shown that other hydrogen-bond donors<br />

can function in place of Asn1219, even if Asn1219 is still present. These groups in HRV14 are the<br />

hydroxyl of Ser1107 and the backbone nitrogen of Leu1106. Other hydrogen-bonding groups are present<br />

in other rhinoviruses that coordinate to tightly bound waters, which can also act as hydrogen-bond<br />

donors [55,56]. This provides a flexible hydrogen-bonding network that can then<br />

http://legacy.netlibrary.com/nlreader/nlReader.dll?bookid=12640&filename=Page_509.html [4/9/2004 12:42:48 AM]

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!