Response to remainder of FDA queries concerning production of [11C](-)RWAY under IND #73,365
1. Explain the rationale for the use of three different UV detection wavelengths
selected for the HPLC systems described. For example, 220 nm for the analytical
HPLC, 240 nm for the prep HPLC and 254 nm for the chiral HPLC systems.
Provide the UV spectrum of (-)RWAY reference standard.
Throughout the CMC section the UV wavelength used for the reverse phase analytical
and prep HPLC methods is 240 nm. The UV detection of (-)-RWAY (see attached
spectrum) and its desmethyl precursor via HPLC is optimal at this wavelength. The chiral
HPLC method uses a wavelength of 254 nm due to the higher absorption coefficient of
triethylamine at 240 nm. Triethylamine is needed in the mobile phase for the chiral
HPLC method in order to reduce tailing and maximize separation of the enantiomers.
Thus, to minimize the background UV absorbance of the mobile phase, a wavelength of
254 nm was selected for the test of enantiomeric.
2. Justify the ± 10% variation range for the retention times of [C-11](-)RWAY and
its reference standard described in the radiochemical identity HPLC test
The variation range that we have specified is to allow for the small changes in the
retention time that can occur when a sample is injected in different media. After
production of [11C](-)RWAY, the radiopharmaceutical is formulated in saline and
injected onto the HPLC column in this medium. The standard, however, is dissolved and
stored in acetonitrile. To ensure that any variability is only a result of sample matrix, the
radiopharmaceutical and the standard are also co-injected each time, although this is not a
release criterion.
3. Provide the certificates of analyses of precursor [desmethyl-(-)-RWAY]and
reference standard [(-)-RWAY] from Axon Biochemicals
Attached
4. The HPLC procedure for optical purity referenced on Tab 1, page 11 (Document
3), is the analytical HPLC system. Please clarify that you will use the chiral
HPLC system for the optical enantiomeric purity
We confirm that the chiral HPLC system is utilized for acceptance testing of every new
batch of precursor and once annually for testing the enantiomeric purity of [11C](-)RWAY. A Chiralpak AD column is dedicated for testing the enantiomeric purity of
[11C](-)-RWAY. Before each analysis of [11C](-)-RWAY, reference (-) and (+) RWAY
will be co-injected onto the chiral column to ensure that the column is able to resolve
both enantiomers.