Modification of Pyrrolo[2,1-a]isoquinolines and Pyrrolo[1,2-a]quinolines with Ammonium Acetate and Dimethyl Sulfoxide via Methylthiomethylation

An efficient methylthiomethylation of pyrroloisoquinolines and pyrroloquinolines has been reached by the use of ammonium acetate and dimethyl sulfoxide. Methylthiomethylated heterocycles can be obtained in moderate to good yields in most cases, while trace amounts to good yields of methylene-bridged products can be observed. Choice of DMSO activator and its amount have a great influence on the chemoselectivity of this process. It is worth noting that this process can also be scalable. Another feature of this process is that the product can be transformed to sulfone and sulfoxide easily.

A possible prebiotic origin on volcanic islands of oligopyrrole-type photopigments and electron transfer cofactors

Tetrapyrroles are essential to basic biochemical processes such as electron transfer and photosynthesis. However, it is not known whether these evolutionary old molecules have a prebiotic origin. We have serendipitously obtained pyrroles, which are the corresponding monomers, in laboratory experiments that simulated the interaction of amino acid-containing seawater with molten lava. The thermal pyrrole formation from amino acids, which so far has only been reported for special cases, can be explained by the observation that the amino acids become metal bonded, for example in (CaCl2)3(Hala)2·6H2O (Hala=DL-alanine), when the seawater evaporates. At a few hundred degrees Celsius, sea salt crusts also release hydrochloric acid (HCl). On primordial volcanic islands, the volatile pyrroles and HCl must have condensed at cooler locations, for example, in rock pools. There, pyrrole oligomerization may have occurred. To study this possibility, we added formaldehyde and nitrite, two species for which plausible prebiotic sources are known, to 2,4-diethylpyrrole and HCl. We found that even at high dilution conjugated (oxidized) oligomers, including octaethylporphyrin and other cyclic and open-chain tetrapyrroles, were formed. All experiments were conducted under rigorously oxygen-free conditions. Our results suggest that primitive versions of present-day biological cofactors such as chlorophylls, bilins, and heme were spontaneously abiotically synthesized on primordial volcanic islands and thus may have been available to the first protocells.

Simple formation of an abiotic porphyrinogen in aqueous solution

Porphyrins have long been proposed as key ingredients in the emergence of life yet plausible routes for forming their essential pyrrole precursor have heretofore not been identified. Here we show that the anaerobic reaction of δ-aminolevulinic acid (ALA, 1-5 mM) with the β-ketoester methyl 4-methoxyacetoacetate (2-40 mM) in water (pH5-7) at 70-100°C for >6 h affords the porphyrinogen, which upon chemical oxidation gives the corresponding porphyrin in overall yield of up to 10%. The key intermediate is the α-methoxymethyl-substituted pyrrole, which undergoes tetramerization and macrocycle formation under kinetic control. The resulting type-I porphyrin bears four propionic acid and four carbomethoxy groups, is distinct from porphyrins (e.g., uroporphyrin or coproporphyrin) derivable from ALA alone via the extant universal biosynthetic path to tetrapyrroles, and is photoactive upon assembly into cationic micelles in aqueous solution. The simple self-organization of eight acyclic molecules into a tetrapyrrole macrocycle, from which a porphyrin is derived that is photoactive in lipid assemblies, augurs well for the spontaneous origin of catalysts and pigments essential for prebiotic metabolism and proto-photosynthesis.

Oligocyclization of 2-(hydroxymethyl)pyrroles with electron-withdrawing groups at β-positions: formation and structural elucidation of porphyrinogens and hexaphyrinogens

Acid-catalyzed oligomerization of 2-(hydroxymethyl)pyrroles bearing C6F5, 2,6-Cl2C6H3, CF3 and CO2Et groups at beta-positions was examined. The reaction of ethyl pyrrole-3-carboxylates gave a mixture of oligomers and type I isomers of porphyrinogens and hexaphyrinogens were isolated when the other beta-substituents were sufficiently bulky, for example, mesityl, 2,6-Cl2C6H3 and C6F5 groups. On the other hand, the pyrroles having other electron-withdrawing groups afforded porphyrinogens as the only isolable products.

1,4-Disubstituted and 1,4,5-Trisubstituted 2-[(Benzotriazol-1-yl)methyl]pyrroles as Versatile Synthetic Intermediates

The CH(2)Bt substituent, unlike previously used CH(2)X substituents, enables (i) the synthetic elaboration of pyrroles with unsubstituted ring positions and (ii) electrophilic as well as nucleophilic substitutions to give pyrroles of type pyrrolyl-2-CHENu. Thus, 1,4-disubstituted (7) and 1,4,5-trisubstituted 2-[(benzotriazol-1-yl)methyl]pyrroles (15) were easily prepared from the reaction of 5-(benzotriazol-1-yl)-1,2-epoxy-3-pentynes 4 or 14 with primary amines in i-PrOH. The 2-(benzotriazol-1-yl)methyl side chains of compounds 7 and 15 were elaborated by nucleophilic substitution and also by initial alkylation followed by replacement or elimination of the benzotriazolyl moiety to afford a variety of 1,2,4-trisubstituted (6, 8-9, 11-13) and 1,2,4,5-tetrasubstituted pyrroles (18, 20-22).