Gentamicin Cla

The solution structures of 1 1 complex between paromomycin and gentamicin Cla and the A-site oligonucleotide have been solved at high resolution using heteronuclear NMR techniques These approaches require the preparation of uniformly labeled N- and C-RNA oligonucleotides via in vitro transcription with labeled nucleoside triphosphates. The use of RNAs labeled with NMR-active nuclei allows for the application of sophisticated heteronuclear NMR methods. These methods facilitate the assigmnent of NMR resonances and the acquisition of structural restraints for detailed structure determinations. 

Additional rings on paromomycin and gentamicin Cla point to a molecular explanation of why 4, 6 -disubstituted aminoglycosides are more specific for the A-site binding pocket and enhance the affinity of aminoglycosides for the decoding site. 

TABLE 8.5. Stability Constants (log fi and pA Values)" of Gentamicin Cla, C2, and Cl Complexes with Copper Ion... 

TABLE 8.6. Stability Constants (log p and pAa Values) of Gentamicin Cla Complexes with Zinc Ion... 

The white powder is a mixture of the sulfate of gentamicin Cla, and the sulfate of XK-62-2, and exhibits an activity of 620 units/mg (the activity of 1 mg of pure product corresponds to 1,000 units). 

A wide variety of natural and synthetic variations is permissible at C5", and at C6" for C 5 branched compounds (41). An extensive study of C6" modificationsof kanamycin B revealed that halogeno, azido, amino, alkylthio, and alkoxy substitutions are all well tolerated until they become very bulky (70). For example, only the N-hexanoyl-N-butylarnino derivative was essentially inactive against all bacteria tested, but the smaller substituents retained good activity. The NMR structure of gentamicin Cla (which is 5 deoxy) indicates that any modification at C 5 would be directed away from 30S (60). The predicted lack of interaction between C5" substituents and 308 explains why a variety of small substitutions is permissible. 

Three of the antibiotics listed in Table 6.1, chloramphenicol, clindamycin, and the synthetic drug linezolid, are expected to have absorption and permeation qualities similar to the vast majority of drugs. All of the compounds that failed had either too many hydrogen bond acceptors, too many hydrogen bond donors, or both. Only two compounds in the failed set, gentamicin Cla and tetracycline, had molecular weights under 500. Many compounds were borderline in particular, tetracycline has six hydrogen bond donors instead of the limit of five, but otherwise satisfies the rule of 5. Note that many active tetracycline derivatives satisfy the rule of 5. 

Figure 7.9 Determination of aminoglycosides in bovine milk fortified at 0.06 ixg/kg as their phenylisocyanate derivatives, by LC-MS analysis (a) [gentamicin Cla(PhIC)5H] (b) [gentamicin C2, 2a(PhIC)5H]+ (c) [gentamicin Cl(PhIC)5H]+ (d) [tobramycin(PhIC)5H]+ (e) [neomycin B(PhIC)6H]+.

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