Enzyme-catalyzed reactions have begun to transform pharmaceutical manufacturing, offering levels of selectivity and tunability that can dramatically improve chemical synthesis. Combining enzymatic reactions into multistep biocatalytic cascades brings additional benefits. Cascades avoid the waste generated by purification of intermediates. They also allow reactions to be linked together to overcome an unfavorable equilibrium or avoid the accumulation of unstable or inhibitory intermediates. We report an in vitro biocatalytic cascade synthesis of the investigational HIV treatment islatravir. Five enzymes were engineered through directed evolution to act on non-natural substrates. These were combined with four auxiliary enzymes to construct islatravir from simple building blocks in a three-step biocatalytic cascade. The overall synthesis requires fewer than half the number of steps of the previously reported routes.

Oral pre-exposure prophylaxis (PrEP) can reduce HIV incidence among at-risk persons. However, for PrEP to have an impact in decreasing HIV incidence, clinicians will need to be willing to prescribe PrEP. HIV specialists are experienced in using antiretroviral medications, and could readily provide PrEP, but may not care for HIV-uninfected patients. Six focus groups with 39 Boston-area HIV care providers were conducted (May-June 2012) to assess perceived barriers and facilitators to prescribing PrEP. Participants articulated logistical and theoretical barriers, such as concerns about PrEP effectiveness in real-world settings, potential unintended consequences (e.g. risk disinhibition and medication toxicity), and a belief that PrEP provision would be more feasible in primary care clinics. They identified several facilitators to prescribing PrEP, including patient motivation and normative guidelines. Overall, participants reported limited prescribing intentions. Without interventions to address HIV providers’ concerns, implementation of PrEP in HIV clinics may be limited.

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To determine if lateral phase separation occurs in films of pulmonary surfactant, we used epifluorescence microscopy and Brewster angle microscopy (BAM) to study spread films of calf lung surfactant extract (CLSE). Both microscopic methods demonstrated that compression produced domains of liquid-condensed lipids surrounded by a liquid-expanded film. The temperature dependence of the pressure at which domains first emerged for CLSE paralleled the behavior of its most prevalent component, dipalmitoyl phosphatidylcholine (DPPC), although the domains appeared at pressures 8-10 mN/m higher than for DPPC over the range of 20-37 degrees C. The total area occupied by the domains at room temperature increased to a maximum value at 35 mN/m during compression. The area of domains reached 25 +/- 5% of the interface, which corresponds to the predicted area of DPPC in the monolayer. At pressures above 35 mN/m, however, both epifluorescence and BAM showed that the area of the domains decreased dramatically. These studies therefore demonstrate a pressure-dependent gap in the miscibility of surfactant constituents. The monolayers separate into two phases during compression but remain largely miscible at higher and lower surface pressures.

Molnupiravir (MK-4482) is an investigational antiviral agent that is under development for the treatment of COVID-19. Given the potential high demand and urgency for this compound, it was critical to develop a short and sustainable synthesis from simple raw materials that would minimize the time needed to manufacture and supply molnupiravir. The route reported here is enabled through the invention of a novel biocatalytic cascade featuring an engineered ribosyl-1-kinase and uridine phosphorylase. These engineered enzymes were deployed with a pyruvate-oxidase-enabled phosphate recycling strategy. Compared to the initial route, this synthesis of molnupiravir is 70% shorter and approximately 7-fold higher yielding. Looking forward, the biocatalytic approach to molnupiravir outlined here is anticipated to have broad applications for streamlining the synthesis of nucleosides in general.