Enzymatic C(sp³)‑H Amination: P450-Catalyzed Conversion of Carbonazidates into Oxazolidinones

Cytochrome P450 enzymes can effectively promote the activation and cyclization of carbonazidate substrates to yield oxazolidinones via an intramolecular nitrene C–H insertion reaction. Investigation of the substrate scope shows that while benzylic/allylic C–H bonds are most readily aminated by these biocatalysts, stronger, secondary C–H bonds are also accessible to functionalization. Leveraging this “non-native” reactivity and assisted by fingerprint-based predictions, improved active-site variants of the bacterial P450 CYP102A1 could be identified to mediate the aminofunctionalization of two terpene natural products with high regio- and stereoselectivity. Mechanistic studies and KIE experiments show that the C–H activation step in these reactions is rate-limiting and proceeds in a stepwise manner, namely, via hydrogen atom abstraction followed by radical recombination. This study expands the reactivity scope of P450-based catalysts in the context of nitrene transfer transformations and provides first-time insights into the mechanism of P450-catalyzed C–H amination reactions

Table_6_Prognostic Factors for Elderly Patients Treated With Stereotactic Body Radiation Therapy for Pancreatic Adenocarcinoma.docx

<p>Introduction: Pancreatic ductal adenocarcinoma (PDAC) commonly presents later in life with a median age at diagnosis of 70 years. Unfortunately, elderly patients are significantly underrepresented in clinical trials. Stereotactic body radiation therapy (SBRT) is a promising treatment modality in this population as it has demonstrated excellent local control with minimal toxicity. We aimed to determine prognostic factors associated with outcomes in elderly patients treated with SBRT.</p><p>Materials and Methods: Elderly patients older than 70 treated with SBRT for PDAC at our institution, from 2004 to 2014 were included. Our primary endpoints included overall survival (OS) and local-progression-free survival (LPFS). Secondary endpoints included regional-progression-free survival (RPFS), distant-progression-free-survival (DPFS) and radiation toxicity. Endpoints were analyzed with the Kaplan-Meier method. The association of these survival endpoints with risk factors was studied with Cox proportional hazards models.</p><p>Results: We identified 145 patients with 146 lesions of pancreatic adenocarcinoma with a median age at diagnosis of 79 (range, 70.1–90.3). SBRT was delivered to a median dose of 36 Gy (IQR 24–36). Surgical resection was performed on 33.8% of the total patients. Median follow-up was 12.3 months (IQR 6.0–23.3 months) and the median survival for the entire cohort 14.0 months with a 2-year OS of 27%. Multivariate analysis (MVA) demonstrated surgery [p ≤ 0.0001, HR 0.29 (95% CI, 0.16–0.51)] and post-SBRT CA19-9 [p = 0.009, HR 1.0004 (95% CI, 1.0002–1.0005)] significantly associated with overall survival. Recurrent lesions [p = 0.0069, HR 5.1 (95% CI, 1.56–16.64)] and post-SBRT CA19-9 levels [p = 0.0107, HR 1.0005 (95% CI, 1.0001–1.0008)] were significantly associated with local control on MVA. For the entire cohort, 4.1% experienced acute grade 2+ toxicity, and 2% experienced late grade 2+ toxicity at 2 years.</p><p>Conclusion: This review demonstrates prognostic factors in elderly patients with PDAC treated with SBRT. We identified surgical resection and post-SBRT CA 19-9 as predictive of overall survival in this population. Additionally, we show low acute and late toxicity following SBRT in elderly patients.</p