Short Communication IMPACT OF PROLONGED REDUCED-PRESSURE CONDITION PRIOR TO PRECURSOR LABELING ON THE LABELING EFFICIENCY OF F-18 FLUOROCHOLINE SYNTHESIS HISHAR H. * , HANAFI M. H., FATHINUL FIKRI A. S. 1 Centre for Diagnostic Nuclear Imaging, Universiti Putra Malaysia, 43400 Serdang, Selangor, Malaysia Email: hishar.hassan@gmail.com Received: 12 Oct 2017 Revised and Accepted: 24 Feb 2018 ABSTRACT Objective: The goal of this preliminary work was to observe the impact of the prolonged reduced-pressure condition prior to labeling stage on the F-18 Fluorocholine labeling yield at the end of synthesis. Methods: At this present work, the condition inside the reactor vial prior to labeling stage was manipulated. In the first technique of syntheses of F- 18 Fluorocholine, the condition inside the reactor vial was set at 0 atmospheric pressure (0 atm) while in the second technique the condition inside the reactor was set at reduced-pressure (between-0.65 to-0.85 bars) with the delay time of 120 seconds. At the end of the synthesis, the impact of the prolonged reduced-pressure condition prior to precursor labeling was measured in terms of labeling yield of F-18 Fluorocholine. Results: With the second technique, the labeling yield of F-18 Fluorocholine was elevated from 9.7% (the first technique) to 24.3%. Conclusion: This preliminary work indicates that delay in a reduced-pressure condition prior to labeling step has greatly improved the labeling yield of F-18 Fluorocholine at the end of synthesis. Using this approach, the labeling yield of F-18 Fluorocholine was elevated from 7.5% to 24.3%. Keywords: Azeotropic drying, F-18 Fluorocholine, Labeling yield, Reduced-pressure © 2018 The Authors. Published by Innovare Academic Sciences Pvt Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/) DOI: http://dx.doi.org/10.22159/ijpps.2018v10i4.23057 N-methyl-(C-11) choline (C-11 choline) was the first choline derivative labeled with positron emitter isotopes [1]. Since then, C-11 choline proved to be an effective marker in various tumors located in brain, lungs, urinary bladder, and most significantly in prostate [1-5]. However, due to the short half-life of radioisotope carbon-11 compared to radioisotope fluorine-18, it becomes a limiting factor to those centres which are not cyclotron-bounded. For this reason, fluorinated labeled choline, N,N-dimethyl-N-(F-18)-fluoromethyl-2-hydroxyethyl ammonium or known as F-18 Fluorocholine, has been developed as a substitute for choline derivatives in Positron Emission Tomography (PET) imaging technique [6-8]. Due to its high positron emission abundance, low positron energy, the small ion radius and its ease of production, fluorine- 18 (F-18) become the most extensively used radioisotope for PET imaging technique. In addition, the half-life of fluorine-18 is relatively long enough to allow for multistep synthesis and transportation to remote hospitals without an on-site cyclotron [9-10]. In 2001, DeGrado had successfully synthesised F-18 Fluorocholine using the reactive intermediate, F-18 fluorobromomethane (F-18 CH2Br) [11-13]. DeGrado’s work was followed by Iwata in 2002 but using F-18 fluoromethyl triflate, a different reactive intermediate [14]. In 2008, Kryza and co-workers had successfully synthesised F-18 Fluorocholine using a similar approach as DeGrado but eliminated the use of semi-preparative HPLC column for purification [15]. In this attempt, F-18 Fluorocholine were synthesised in accordance with Kryza method on an automated synthesis platform, GE TracerLab MXFDG [15]. It is known the limiting factor that affects the F-18 Fluorocholine production around the globe, is due to its relatively low yield. Therefore, this preliminary works attempt to investigate whether a prolonged reduced-pressure condition prior to labeling step will affect the yield of F-18 Fluorocholine. Fig. 1: Synthesis of F-18 fluorocholine At the present works, two techniques were employed to observe the impact of the prolonged reduced-pressure condition on the yield of F-18 Fluorocholine. In the first technique, during the syntheses of F-18 Fluorocholine (n = 3), succeeding to F-18 ions elution to reactor vial, the condition inside the reactor was set at 0 atmospheric pressure (0 atm). Meanwhile, in the second International Journal of Pharmacy and Pharmaceutical Sciences ISSN- 0975-1491 Vol 10, Issue 4, 2018