Mazen Es-Sayed

New Efficient Multicomponent Reactions with C−C Coupling for Combinatorial Application in Liquid and on Solid Phase

Up to nine C-C bonds are formed selectively from up to seven components starting from an alkene, a haloarene, and a dienophile [Eq. (1)]. A comparison of liquid- and solid-phase reactions reveals a surprising superiority of the solid-phase reaction.

Imidazo[5,1-f][1,2,4]triazin-4(3H)-ones, a new class of potent PDE 5 inhibitors

2-aryl-substituted imidazo[5,1-f][1,2,4]triazin-4(3H)-ones represent a new class of potent cGMP-PDE 5 inhibitors that prove to be superior to other purine-isosteric inhibitors. Subnanomolar inhibitors of PDE 5 with activity in in vivo models for erectile dysfunction have been identified. BAY 38-9456 (Vardenafil-hydrochloride) has been selected for clinical studies in the indication of erectile dysfunction.

A new highly efficient three-component domino Heck-Diels-Alder reaction with bicyclopropylidene: rapid access to spiro[2.5]oct-4-ene derivatives.

Bicyclopropylidene (1) was found to surpass even methyl acrylate (17 a) in its rate of undergoing carbopalladation with aryl- or alkenylpalladium species, leading to substituted allylidenecyclopropanes 5, 7 and 10, mostly in high yields (37-78 %). These dienes and cross-conjugated trienes react in a Diels-Alder mode with dienophiles to give spiro[2.5]octenes 18 a-Ph, 18 b-Ph and 18 a-Vin, respectively, in good yields (89, 69 and 65 %). The overall transformation can be achieved as a one-pot three-component reaction with a variety of dienophiles to furnish the domino Heck-Diels-Alder products 18 regioselectively in most cases in good to very high yields (49-100 %). The reaction of 1 with iodobenzene (2-Ph) and 17 a gave 18 a-Ph in virtually quantitative yield-also on a gram scale-using only 1 mol % of catalyst, and even bromobenzene (22) gave 18 a-Ph in 59 % yield. Bicyclopropylidene (1), in the presence of palladium acetate/triphenylphosphane underwent rearrangement to allylidenecyclopropane (5-H), which in turn dimerized (73 %) in the absence of other reaction partners, or could be trapped by diethyl fumarate (17 c) to give the Diels-Alder adduct 18 c-H in 45 % yield. The coupling of oligoiodobenzenes with 1 and subsequent cycloaddition could be extended to a multicomponent reaction. In this way, 1,4-diiodobenzene (37), 1 and an alkyl acrylate gave the products 38 of a twofold Heck-Diels-Alder reaction in up to 87 % yield, 1,3,5-triiodobenzene (39) reacted in up to 72 % yield and ultimately 1,2,4,5-tetraiodobenzene (41) gave the fourfold domino Heck-Diels-Alder product 42 in 47 % isolated yield, in a single operation in which 12 new carbon-carbon bonds were formed.

TOTAL SYNTHESIS OF TAN-1057 A/B, A NEW DIPEPTIDE ANTIBIOTIC FROM FLEXIBACTER SP. PK-74

TAN-1057 (1a, b) − a new natural dipeptide antibiotic active against methicillin resistant strains of Staphylococcus aureus − was synthesized starting from Nα, Nδ, Nω-tri-Z-L-arginine 20b via the corresponding diazoketone 21b. This upon photolysis rearranged to the ketene which was trapped by (±)-2,4,5,6-tetrahydro-5-methylamino-2-ureidopyrimidin-4-one (3) to yield the fully protected dipeptide 23 (30%). The latter was deprotected by hydrogenolysis to give the final compound as a mixture of two epimers − TAN-1057A, B − isolated previously from a strain of Flexibacter sp. PK-74. The intermediate 3 was prepared from 3-amino-2-(N-Z-N-methylamino)propionic acid methyl ester hydrochloride (16) and 2-methyl-2-thiopseudobiuret hydroiodide (18) in one step in 35% yield.

3‐Azabicyclo[3.1.0]hex‐1‐ylamines by Ti‐Mediated Intramolecular Reductive Cyclopropanation of α‐(N‐Allylamino)‐Substituted N,N‐Dialkylcarboxamides and Carbonitriles

A variety of tris- and monoprotected derivatives with the 1-amino-3-azabicyclo[3.1.0]hexane and 1-amino-3-azabicyclo[4.1.0]heptane skeleton 10 have been synthesized by intramolecular reductive cyclopropanation of α-(N-allylamino)-substituted N,N-dialkylcarboxamides 6, 8, and 9. Starting from derivatives of the naturally occurring amino acid serine (4a, 4b), the enantiomerically pure compounds 10a and 10b were obtained with endo/exo ratios of 2.5:1 (a) and 2:1 (b), in 26 and 30% overall yields, respectively. The unprotected bicyclic amines 11aa, 11ab, 11ba, and 11ad have been prepared by palladium-catalyzed hydrogenative deprotection of 10aa, 10ab, 10ba and 10ad, respectively, under acidic conditions, in 91, 95, 96, and 99% yields, respectively. X-ray crystal structure analyses of 10aa and 10ad in each case found an equatorial position of the N-benzyl group on the heterocycle and a common boat conformation for the 3-azabicyclo[3.1.0]hexane and 3-azabicyclo[4.1.0]heptane skeletons as a whole. One-step preparations of the bicyclic diamines 11ac (41% yield) and 14a (48% yield) have been performed by application of the Kulinkovich−de Meijere procedure to the nitriles 12a and 12b. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

A New and Efficient Access to Thiazoline‐4‐carboxylates and Cysteine Derivatives Incorporating Cyclopropyl Groups

Under basic conditions (NaHCO3, MeCN), thiocarboxamides 2, including N,N-thioureas, cleanly undergo Michael addition onto 2-chloro-2-cyclopropylideneacetates 1, attacking through the sulfur, and this is followed by an intramolecular substitution to afford 5-spirocyclopropane-annelated thiazoline-4-carboxylates 4 in 37−92% yields. The thiazolines 4 are cysteine derivatives that possess a cyclopropyl or substituted cyclopropyl group in place of the gem-dimethyl-substituted β-carbon atom of penicillamine; they can be hydrolyzed to the hydrochloride salt of the amino acid 5 by heating in acid. Under acidic conditions (CH2Cl2, HCl), the Michael adducts 7 of thioamides 2 onto 1 are formed in high to virtually quantitative yields. When treated with NaHCO3 in MeCN, the adducts 7 cyclize to thiazolinecarboxylates 4 (51−82%), but in the presence of Ti(OiPr)4 they form spirocyclopropane-annelated thiazinones 8 (19−88%).

Solid supported fluoronitroaryl triazenes as immobilized and convertible Sanger reagents – synthesis and SNAr reactions towards a novel preparation of 1-alkyl-5-nitro-1H-benzotriazolesElectronic supplementary information (ESI) available: experimental procedures. See http://www.rsc.org/suppdata/cc/b2/b201489k/

Synthesis of novel fluoronitroaryl triazenes in liquid phase and on solid support have been described; mild displacement of the fluoride ion with various nucleophiles provides access to substituted arenes which in turn can be cleaved to provide a unique access to 1-alkyl-5-nitro-1H-benzotriazole.

Synthesis and biological activity of simplified belactosin C analogues

Successful biochemical studies of the natural products belactosin A and C and their acylated congeners have shown a β-lactonecarboxamide moiety to be a possible core structure of powerful proteasome inhibitors. As a part of further investigations, variously decorated simplified β-lactonecarboxamides have been synthesized in order to understand structure-biological activity relations in detail, to find ways of improving their biological activity and stability and to reduce the complexity of their preparation. Biological tests showed that the best compounds possess a high potential against phytopathogenic fungi in the greenhouse.

High yielding selective access to spirocyclopropanated 5-oxopiperazine-2-carboxylates and 1,4-diazepane-2,5-diones from methyl 2-chloro-2-cyclopropylideneacetate.

The 2-spirocyclopropanated methyl 5-oxopiperazine-2-carboxylate and the 3-spirocyclopropanated 6-chloro-1,4-diazepane-2,5-dione could both be prepared at choice in 93 and 88% yield, respectively, from methyl 2-chloro-2-cyclopropylideneacetate () in a sequence of Michael addition of 3-benzyloxypropylamine, peptide coupling with N-Boc-glycine, Boc-group removal and cyclization. Transformation of the benzyloxypropyl side chain, peptide coupling with N-Boc-(S)-asparagine, deprotection and repeated cyclization led to the octahydro[2H]pyrazino[1,2-a]pyrazinetrione scaffold containing a rigidified mimic of a tripeptide with a DGR motif. The overall yield of after deprotection of (a total of 13 steps in 8 distinct operations) was 30%.

AN ASYMMETRIC SYNTHESIS OF NOVEL AMINOCYCLOPROPYL CARBOXYLIC ACIDS (ACC)

Cyclopropanation of chiral bicyclic lactams 2 followed by removal of the chiral auxiliary and a Curtius rearrangement leads to the title compounds in >99% e.e.