7-Azabicycloheptane carboxylic acid: a proline replacement in a boroarginine thrombin inhibitor

Introduction of C(5/6) side chains onto 2-azabicyclo[2.1.1]hexanes via a 6-anti-bromo-5-anti-hydroxy derivative

Oxidation of the title bromoalcohol provided the strained ketone, 5-bromo-6-oxo-2-azabicyclo[2.1.1]hexane. Additions of nucleophiles to either this or the debrominated ketone have been used to introduce 5(6)-syn-alkyl and aryl groups, 5(6)-alkylidene linkages, and 5(6)-anti-alkyl and acyl substituents. Facial selectivity is for additions to the 6-bromo-5-ketone and 5-alkylidene azabicycles to occur from the face syn to the nitrogen atom. The bromine atom of the title alcohol has also been replaced by a 6-anti-(1-hydroxyethyl) substituent using a directed radical addition process. The stereoselective functionalization reactions expand the range of available methano-bridged pyrrolidines.

5(6)-anti-Substituted-2-azabicyclo[2.1.1]hexanes: a nucleophilic displacement route

Nucleophilic displacements of 5(6)-anti-bromo substituents in 2-azabicyclo[2.1.1]hexanes (methanopyrrolidines) have been accomplished. These displacements have produced 5-anti-X-6-anti-Y-difunctionalized-2-azabicyclo[2.1.1]hexanes containing bromo, fluoro, acetoxy, hydroxy, azido, imidazole, thiophenyl, and iodo substituents. Such displacements of anti-bromide ions require an amine nitrogen and are a function of the solvent and the choice of metal salt. Reaction rates were faster and product yields were higher in DMSO when compared to DMF and with CsOAc compared to NaOAc. Sodium or lithium salts gave products, except with NaF, where silver fluoride in nitromethane was best for substitution by fluoride. The presence of electron-withdrawing F, OAc, N(3), Br, or SPh substituents in the 6-anti-position slows bromide displacements at the 5-anti-position.

A new constrained proline analogue with an 8-azabicyclo[3.2.1]octane skeleton

A straightforward synthesis of 8-azabicyclo[3.2.1]octane-1-carboxylic acid, a new proline analogue with a bicyclic structure, is described. The procedure makes use of readily available starting materials and involves simple, high-yielding transformations.

Salicylaldimine dimers derived from 2-H2NC6H4Bpin (pin = 1,2-O2C2Me4)

Condensation of salicylaldehyde (2-HOC6H4C(O)H) with 2-H2NC6H4Bpin (pin = 1,2-O2C2Me4) afforded the macrocyclic dimer 1 with an OBOBO structural unit. Similar reactivity with substituted salicylaldehyde derivatives gave the corresponding Schiff bases 2–6. Crystals of 1 were triclinic, space group P-1, a = 9.7915(4) Å, b = 10.8569(5) Å, c = 12.8445(6) Å, α = 102.067(1)°, β = 96.011(1)°, γ = 90.458(1)°, Z = 2. All new compounds have been tested for their antifungal activity against Aspergillus niger and Aspergillus flavus.Key words: antifungal, boron, dehydration, heterocycles, Schiff bases.

Platinum pyridinecarboxaldimine complexes containing boronate esters

Condensation of 2-pyridinecarboxaldehydes with 2-, 3-, and 4-H2NC6H4Bpin (pin = 1,2-O2C2Me4) gave the corresponding boron-containing pyridinecarboxaldimines (N–NBpin). Addition of these ligands to [PtCl2(coe)]2 (coe = cis-cyclooctene) gave complexes of the type cis-PtCl2(N–NBpin) in moderate yields. The platinum complexes have been examined for their potential cytotoxicities against OV2008 (human ovarian carcinoma) and the analogous cisplatin-resistant cell line C13. Key words: boronate esters, pyridinecarboxaldimines, cytotoxicity, platinum, boron.

Convenient preparations of 2,4-methanopyrrolidine and 5-carboxy-2,4-methanopyrrolidines

An efficient four-step synthesis of N-BOC-5-syn- and 5-anti-carboxymethanopyrrolidines (12 and 13) and the conversion of 12 to N-BOC-methanopyrrolidine (2) are described.

Synthesis of enantiomerically pure 1,2-diamine derivatives of 7-azabicyclo[2.2.1]heptane. New leads as glycosidase inhibitors and rigid scaffolds for the preparation of peptide analogues

Enantiomerically pure alcohols (-)- and (+)-7-tert-butoxycarbonyl-6-endo-p-toluenesulfonyl-7-azabicyclo[2.2.1]hept-2-en-5-endo-ol ((-)-11 and (+)-11) have been obtained from the Diels-Alder adduct of N-(tert-butoxycarbonyl)pyrroel and 2-bromo-1-p-toluenesulfonylacetylene, including a resolution method. These two alcohols were converted into (+)- and (-)-5-exo-amino-7-(tert-butoxycarbonyl)-2,3-exo-isopropylidenedioxy-7-azabicyclo[2.2.1]heptane ((+)-18 and (-)-18) and (+)- and (-)-5-endo-amino-7-(tert-butoxycarbonyl)-2,3-exo-isopropylidenedioxy-7-azabicyclo[2.2.1]heptane ((+)-19 and (-)-19) after adequate functionalization and desulfonylation steps. The corresponding conformationally constrained bicyclic 1,2-diamines (+)-4, (-)-4, (+/-)-5, (+/-)-6, (+)-7, and (-)-7 were obtained from the protected precursors 18 and 19 and evaluated as glycosidase inhibitors. Diamines (+)-4, (-)-4, (+)-6, and (-)-6 can be seen as new nonpeptide molecular scaffolds for the design of peptide analogues.

Complex-induced proximity effects. Temperature-dependent regiochemical diversity in lithiation-electrophilic substitution reactions of N-BOC-2-azabicyclo[2.1.1]hexane. 2,4- and 3,5-methanoprolines

[reaction: see text] Azabicycle 4 and sec-butyllithium/TMEDA afford the C(1) bridgehead alpha-lithio anion at 0 degrees C. Anion quenching with carbon dioxide, methyl chloroformate, or DMF provide the bridgehead acid 8a (N-BOC-2,4-methanoproline), ester 8b, or aldehyde 8c, respectively. By contrast, at -78 degrees C these same reagents give a mixture of regioisomeric methylene and bridgehead anions whose quenching leads to mixtures of regioisomeric methylene and bridgehead acids 6a/8a, esters 6b/8b, or aldehydes 6c/8c, respectively. The previously unknown 3,5-methanoproline was prepared as its N-BOC methyl ester 6b.

Synthesis and reactivity of palladium and platinum diimine complexes containing boronate esters

Condensation of α-diketones (2,3-butanedione, benzil, and acenaphthenequinone) with 3-H2NC6H4Bpin (pin = 1,2-O2C2Me4) gave the corresponding boron-containing α-diimines. The addition of these ligands to [MCl2(coe)]2 (coe = cis-cyclooctene, M = Pd or Pt) gave complexes of the type cis-MCl2(α-diimine) in moderate to high yields. The platinum complexes have been examined for their ability to bind to DNA using enzyme digest studies. These complexes were found to bind to single-stranded DNA as well as, or better than, the non-boron containing controls, and showed binding similar to that of cisplatin (cis-PtCl2(NH3)2).Key words: boronate esters, diazabutadienes, DNA-binding, platinum.

The rearrangement route to 3-CH(2)X-2-azabicyclo[2.1.1]hexanes. Substituent control of neighboring group participation

The stereocontrolled synthesis of a functionalized 3-hydroxymethyl-2-azabicyclo[2.1.1]hexane synthon for a variety of methano-bridged pyrrolidines has been effected. The key step in an electrophilic addition-rearrangement route uses a 3-nosyloxymethyl group in the 2-azabicyclo[2.2.0]hex-5-ene precursor in order to suppress unwanted competitive oxygen neighboring group participation. [reaction: see text]

Synthesis and reactivity of novel Schiff bases containing boronate esters

Condensation of 2-aminophenol with boronate ester derivatives of benzaldehyde afforded the corresponding boron-containing Schiff bases, 2-HOC6H4N=C(H)C6H4R (1a: R = 2-Bpin; 1b: R = 3-Bpin; 1c: R = 4-Bpin; pin = 1,2-O2C2Me4). Crystals of 1b were triclinic, space group P[Formula: see text], a = 11.9420(6), b = 13.0871(7), and c = 13.2720(7) Å, α = 70.983(1), β = 67.793(1), and γ = 78.380(1)°, Z = 2. Reaction of 2-aminophenol with 2-HC(O)C6H4B(OH)2 in EtOH, however, gave a macrocyclic dimer 2 with a OBOBO structural unit. The molecular structure of this dimer has been confirmed by an X-ray diffraction study. Crystals of 2 were monoclinic, space group P21/c, a = 10.0447(8), b = 21.0894(15), and c = 12.6214(9) Å, β = 105.301(2)°, Z = 4. Further reaction of these Schiff bases with manganese triacetate in toluene afforded 2-arylbenzoxazoles 3a–c via an oxidative cyclization pathway. The molecular structure of the 4-Bpin derivative (3c) was characterized by an X-ray diffraction study. Crystals of 3c were monoclinic, space group P21/n, a = 6.5392(3), b = 16.3330(8), and c = 16.1942(8) Å, β = 97.9620(10)°, Z = 4.Key words: boron heterocycles, Schiff bases, arylbenzoxazoles.

New advances in the discovery of thrombin and factor Xa inhibitors

The search for the ideal anticoagulant has spanned decades and has resulted in several strategies including the clinical use of heparin, low molecular weight heparins, and the vitamin K antagonist warfarin. Over the past five years, many groups have reported preclinical results with direct-acting thrombin inhibitors and several of these are now moving into clinical trials. In addition, many groups have disclosed the discovery of potent, orally bioavailable factor Xa inhibitors. Several of these compounds are now in early clinical trials and the results are forthcoming.