Continuous Flow Generation of Acylketene Intermediates via Nitrogen Extrusion.

A flow chemistry process for the generation and use of acylketene precursors through extrusion of nitrogen gas is reported. Key to the development of a suitable continuous protocol is the balance of reaction concentration against pressure in the flow reactor. The resulting process enables access to intercepted acylketene scaffolds using volatile amine nucleophiles and has been demonstrated on the gram scale. Thermal gravimetric analysis was used to guide the temperature set point of the reactor coils for a variety of acyl ketene precursors. The simultaneous generation and reaction of two reactive intermediates (both derived from nitrogen extrusion) is demonstrated.

Integrated Batch and Continuous Flow Process for the Synthesis of Goniothalamin.

An integrated batch and continuous flow process has been developed for the gram-scale synthesis of goniothalamin. The synthetic route hinges upon a telescoped continuous flow Grignard addition followed by an acylation reaction capable of delivering a racemic goniothalamin precursor (16) (20.9 g prepared over 3 h), with a productivity of 7 g·h-1. An asymmetric Brown allylation protocol was also evaluated under continuous flow conditions. This approach employing (-)-Ipc2B(allyl) provided an (S)-goniothalamin intermediate in 98% yield and 91.5% enantiomeric excess (ee) with a productivity of 1.8 g·h-1. For the final step, a ring-closing metathesis reaction was explored under several conditions in both batch and flow regimes. In a batch operation, the Grubbs second-generation was shown to be effective and highly selective for the desired ring closure product over those arising from other modes of reactivity, and the reaction was complete in 1.5 h. In a flow operation, reactivity and selectivity were attenuated relative to the batch mode; however, after further optimization, the residence time could be reduced to 16 min with good selectivity and good yield of the target product. A tube-in-tube reactor was investigated for in-situ ethylene removal to favor ring-closing over cross-metathesis, in this context. These results provide further evidence of the utility of flow chemistry for organometallic processing and reaction telescoping. Using the developed integrated batch and flow methods, a total of 7.75 g of goniothalamin (1) was synthesized.

Impact of continuous flow chemistry in the synthesis of natural products and active pharmaceutical ingredients.

We present a comprehensive review of the advent and impact of continuous flow chemistry with regard to the synthesis of natural products and drugs, important pharmaceutical products and definitely responsible for a revolution in modern healthcare. We detail the beginnings of modern drugs and the large scale batch mode of production, both chemical and microbiological. The introduction of modern continuous flow chemistry is then presented, both as a technological tool for enabling organic chemistry, and as a fundamental research endeavor. This part details the syntheses of bioactive natural products and commercial drugs.

Formal Total Synthesis of Actinoranone: Synthesis Approaches and Cytotoxic Studies.

This article describes our efforts toward the total synthesis of actinoranone. Our synthesis strategies rely on a convergent route to connect the terpenoid and polyketide fragments, employing catalysis and powerful classical reactions for the assembly of these key fragments. A new transformation was disclosed during this work, a domino ring-opening and esterification. Initial cytotoxic studies for the selected synthesis intermediates are also presented.

Formal Total Synthesis of Actinoranone and Asymmetric Synthesis of Labda-7,13-(E)-dien-15-ol.

The syntheses of the polyketide and terpenoid fragments of actinoranone are reported in a concise fashion, relying on catalytic methods. Minimization on the use of protecting groups and redox reactions allowed the synthesis of the carbon backbone of actinoranone in 20 steps (11 steps for LLS). The asymmetric synthesis of labda-7,13-(E)-dien-15-ol is also disclosed.

Design and synthesis of cenocladamide analogues and their evaluation against breast cancer cell lines.

This work describes the total synthesis of the alkaloid cenocladamide and a concise library of nine structural analogues aiming at their evaluation against the breast cancer cell line MDA-MB-231. The most promising compound (3; IC50 = 6.6 µM) was also evaluated in a panel of seven breast cancer cell lines and two non-tumorigenic cell lines. We further conducted an initial investigation on the mechanism of action of analogue 3, which lacks the endocyclic double bond when compared to cenocladamide. The present study presents the discovery of a cenocladamide analogue with interesting cytotoxic activity, which could be useful for further optimization towards new chemotherapeutic agents for breast cancer treatment.

Flow chemistry syntheses of natural products.

The development and application of continuous flow chemistry methods for synthesis is a rapidly growing area of research. In particular, natural products provide demanding challenges to this developing technology. This review highlights successes in the area with an emphasis on new opportunities and technological advances.