Axinastatin 3 as a potential anticancer agent was synthesized by chemical methods. In an electrospray ion-trap mass spectrometer, using one stage of tandem mass spectrometry (MS/MS), the linear peptide intermediate was sequenced via the complementarities of y and b ions. Then, using multistep MS/MS (to MS6), the cyclic peptide was sequenced through sequentially removing one amino acid residue in each stage of MS/MS. The difference of the fragmentation mechanisms and the sequencing approaches between them is discussed.
Two heptapeptides have been prepared by Fmoc methodology using Wang resin as solid support. For attachment of the first amino acid, several coupling systems were evaluated, and DIC/DMAP system could give yields of >99% and low levels of racemization. The selection of scavenger combination to deprotect side chains revealed that H2O/p-cresol was good at scavenging trityl and 1,2-ethanedithiol was highly efficient for scavenging t-butyl. Through shortening the preactivation time to 5 min, the racemization which occurred during formation of amide bonds coupled by HBTU was minimized. The crude peptides were characterized by RP-HPLC and MS, and sequenced by MS/MS to acquire reliable amino acid sequence information.
Background: Thyroid-stimulating hormone (TSH) and free thyroxine (FT4) reference intervals are essential for screening and diagnosing thyroid dysfunction during pregnancy. The aim of this study was to establish method- and trimester-specific TSH and FT4 reference intervals in pregnant Chinese women using the Beckman Coulter UniCel™ DxI 600.
Methods: A cross-sectional dataset analysis was performed. A total of 3507 participants were recruited, and 2743 were eligible for analysis to set reference intervals. TSH, FT4, and thyroid peroxidase antibody (TPOAb) levels were analyzed with the Beckman Coulter UniCel™ DxI 600 Access® immunoassay system. Ranges between the 2.5th and 97.5th percentiles were defined as reference intervals for TSH and FT4.
Results: The calculated reference intervals for the first, second, and third trimesters were TSH: 0.06–3.13, 0.07–4.13 and 0.15–5.02 mIU/L, respectively, and FT4: 8.72–15.22, 7.10–13.55 and 6.16–12.03 pmol/L, respectively.
Conclusions: Our reference intervals for TSH and FT4 are distinct from the ranges reported in the DxI 600 instruction manual and previously reported data, confirming the importance of method-specific reference intervals.