Biomimetic synthesis and biological evaluation of Aplidiopsamine A

Environmentally friendly domino multicomponent strategy for the synthesis of pyrroloquinolinone hybrid heterocycles

An efficient and elegant assembly of pyrene/aryl fused pyrrolo[2,3-b]quinolinone and pyrrolizino[3,2-b]quinolinone hybrid heterocycles was achieved via a domino multicomponent reaction strategy using a solid state melt reaction (SSMR) condition. The 1,3-dipole component was generated in situ from N-methylgylcine/l-proline and isatin, while the Baylis-Hillman adduct prepared from pyrene-1-carbaldehyde and various benzaldehydes is used as the dipolarophile. The domino protocol comprises 1,3-dipolar cycloaddition and a consequent double annulation reaction process. The advantages of this cascade protocol include environmentally friendly conditions, the avoidance of toxic organic solvents, simple work-up and good to excellent product yields.

Total synthesis of pyrrolo[2,3-c]quinoline alkaloid: trigonoine B

The first total synthesis of the pyrrolo[2,3-c]quinoline alkaloid trigonoine B (1) was accomplished via a six-step sequence involving the construction of an N-substituted 4-aminopyrrolo[2,3-c]quinoline framework via electrocyclization of 2-(pyrrol-3-yl)benzene containing a carbodiimide moiety as a 2-azahexatriene system. The employed six-step sequence afforded trigonoine B (1) in 9.2% overall yield. The described route could be employed for the preparation of various N-substituted 4-aminopyrroloquinolines with various biological activities.

Formation of 6-Azaindoles by Intramolecular Diels-Alder Reaction of Oxazoles and Total Synthesis of Marinoquinoline A

A new variant of the intramolecular Diels-Alder oxazole (IMDAO) cycloaddition that provides direct access to 6-azaindoles was developed. The IMDAO reaction was applied in a total synthesis of the aminophenylpyrrole-derived alkaloid marinoquinoline A, also featuring the use of a Curtius reaction for preparation of a 5-aminooxazole, a propargylic C,H-bond insertion, an in situ alkyne-allene isomerization, and a ruthenium-catalyzed cycloisomerization for benzene ring annulation to the 6-azaindole.

Total Synthesis of Hinduchelins A-D, Stereochemical Revision of Hinduchelin A, and Biological Evaluation of Natural and Unnatural Analogues

Here, we report the first total synthesis of hinduchelins A-D, a family of nontoxic catechol derivatives from Streptoalloteichus hindustanus, possessing a druglike chemotype and modest iron-chelating ability. A concise synthesis was developed employing methyl 5-methyloxazole-4-carboxylate as a single starting material to provide hinduchelins A-D (and unnatural analogues) in only four steps and 5-15% overall yields; moreover, the stereochemistry of hinduchelin A was reassigned from ( S) to ( R). Biological evaluation confirmed that natural and unnatural hinduchelins are weak iron chelators (siderophores).

Natural products as modulators of the cyclic-AMP pathway: evaluation and synthesis of lead compounds

It is now well recognized that the normal cellular response in mammalian cells is critically regulated by the cyclic-AMP (cAMP) pathway through the appropriate balance of adenylyl cyclase (AC) and phosphodiesterase-4 (PDE4) activities. Dysfunctions in the cAMP pathway have major implications in various diseases like CNS disorders, inflammation and cardiac syndromes and, hence, the modulation of cAMP signalling through appropriate intervention of AC/PDE4 activities has emerged as a promising new drug discovery strategy of current interest. In this context, synthetic small molecules have had limited success so far and therefore parallel efforts on natural product leads have been actively pursued. The early promise of using the diterpene forskolin and its semi-synthetic analogs as AC activators has given way to new leads in the last decade from novel natural products like the marine sesterterpenoids alotaketals and ansellones and the 9,9'-diarylfluorenone cored selaginpulvilins, etc. and their synthesis has drawn much attention. This review captures these contemporary developments, particularly total synthesis campaigns and structure-guided analog design in the context of AC and PDE-4 modulating attributes and the scope for future possibilities.

Muscarine, imidazole, oxazole and thiazole alkaloids

Covering: July 2012 to June 2015. Previous review: Nat. Prod. Rep., 2013, 30, 869-915The structurally diverse imidazole-, oxazole-, and thiazole-containing secondary metabolites are widely distributed in terrestrial and marine environments, and exhibit extensive pharmacological activities. In this review the latest progress involving the isolation, biological activities, and chemical and biogenetic synthesis studies on these natural products has been summarized.

Sequential hydroarylation/Prins cyclization: an efficient strategy for the synthesis of angularly fused tetrahydro-2H-pyrano[3,4-c]quinolines

Various aldehydes undergo a smooth cascade cyclization with N-(5-hydroxypent-2-yn-1-yl)-4-methyl-N-phenylbenzenesulfonamide in the presence of 10 mol% Ph₃PAuCl/AgSbF₆/In(OTf)₃ to furnish the corresponding tetrahydro-2H-pyrano[3,4-c]quinoline derivatives.

Marine natural products

This review covers the literature published in 2012 for marine natural products, with 1035 citations (673 for the period January to December 2012) referring to compounds isolated from marine microorganisms and phytoplankton, green, brown and red algae, sponges, cnidarians, bryozoans, molluscs, tunicates, echinoderms, mangroves and other intertidal plants and microorganisms. The emphasis is on new compounds (1241 for 2012), together with the relevant biological activities, source organisms and country of origin. Biosynthetic studies, first syntheses, and syntheses that lead to the revision of structures or stereochemistries, have been included.

Towards the Total Synthesis of Marineosin A: Construction of the Macrocyclic Pyrrole and an Advanced, Functionalized Spiroaminal Model

Herein, we describe the enantioselective construction of the 12-membered macrocyclic pyrrole core 4 of marineosin A in 5.1% overall yield from (S)-propylene oxide. The route features a key Stetter reaction to install a 1,4-diketone, which is then subjected to Paal-Knorr pyrrole synthesis and ring closing metathesis (RCM) to afford macrocycle 4. A divergence point in the synthetic scheme also enabled access to a highly functionalized spiroaminal model system 8 via an acid-mediated hydroxyketoamide cyclization strategy.