Natural products studies of the marine cyanobacterium Lyngbya majuscula

The marine cyanobacterium Lyngbya majuscula has proven to be extraordinarily rich in bioactive secondary metabolites. This dissertation describes the chemistry of L. majuscula collected from Grenada, Fiji and Papua New Guinea, and the biosyntheses of two L. majuscula metabolites, curacin A and barbamide. The chemical studies with a Grenada collection of L. majuscula revealed three new metabolites, grenadadiene, debromogrenadadiene and grenadamide. These three compounds are the only reported cyclopropyl-containing fatty acids from Lyngbya species. The chemistry of a mixed assemblage ofL. majuscula/Schizothrix species from Fiji was investigated and shown to contain two novel depsipeptides, yanucamides A and B. Both compounds possessed the unique 2,2-dimethyl-3-hydroxy-7-octynoic acid, a unit that has only been described in the structures ofkulolide-1 and kulokainalide-1, metabolites from the marine mollusk Philinopsis speciosa. Chemical investigation of the highly brine shrimp toxic extract of Papua New Guinea collection of L. majuscula led to the isolation of the previously described cytotoxins, curacins A and D. Upon further investigation ofthe same extract, two new depsipeptides, clairamide and carliamide, were discovered. Clairamide contains 3-amino2-methyl-pentanoic acid, a component unique to cyanobacterial metabolites, while carliamide possesses the 3-amino-2-methyl-7-octynoic acid, a unit that has only been found in the structure of onchidin A, a metabolite from the marine mollusk Onchidium sp. Biosynthetic investigations of barbamide, a unique trichloromethyl-containing metabolite, were carried with the cultured L. majuscula. Results from the feeding experiments have established the biosynthetic units ofthe compound. In addition, isotope-incorporation studies also revealed that barbamide biosynthesis involves chlorination that exclusively occurs at the unactivated pro-S methyl group of leucine. The biosynthesis of curacin A was also examined. Stable isotope feeding experiments have illustrated the cysteine-initiated (or a thiazoline acyl CoA-initiated) polyketide chain assembly of curacin A with C 17 and the OCH₃ arising from methionine. Moreover, the labeling pattern of acetate at C 18-C22 of curacin A is consistent with the five-carbon unit deriving from a branched triketide-derived precursor or isopentyl diphosphate (IPP)/dimethylallyl diphosphate (DMAPP)

Processing of Frozen Parboiled Rice Product

ABSTRACT Laboratory parboiled rice was frozen using two different freezing processes. One process was immersing the sample in liquid nitrogen (N-freezing process), then keeping it at -20°C, and the other process was direct freezing in the freezer at -20°C (F-freezing process) and keeping it there. Samples were then stored for 7 days. Comparison of various properties of cooked frozen rice samples from the two different freezing processes were done using Differential Scanning Calorimetry (DSC) to determine the thermal requirements for starch retrogradation. Hardness value of both methods increased from fresh cooked parboiled rice until day 3 after which the hardness value decreased and showed non significant difference for the freeze-thaw samples at day 7. Starch retrogradation by DSC of N-freezing process caused less enthalpy to melt the starch crystalline material than F-freezing process, especially when the time of storage and the freeze-thaw cycles of rice samples increased, but the difference was non significant for sensory evaluations. Frozen parboiled spicy rice products were processed for comparison by contact plate freezer (C-freezing process) and cryogenic freezer using liquid nitrogen as batch system (N-freezing process) before keeping in a freezer at -20°C for 5 days, and then freeze-thawed everyday. Hardness value of both frozen parboiled spicy rice processes increased from fresh cooked rice until day 3, after which the hardness values decreased and showed non significant difference for the freeze-thaw samples at day 5. There were no significant differences in sensory evaluations

(2S)-2-(3-Oxo-1,4-dioxaspiro­[4.5]decan-2-yl)ethanoic acid

The title compound, C10H14O5, is an inter­mediate in our study of the asymmetric synthesis of α-hydroxy­alkanoic acids. The structure consists of 1,4-dioxaspiro[4,5]decane skeleton formed when the cyclohexylidene group binds to both of the hydroxyl groups of carboxylic groups of the starting malic acid. The six-membered ring adopts a chair conformation

Single Cell Genome Amplification Accelerates Identification of the Apratoxin Biosynthetic Pathway from a Complex Microbial Assemblage

Filamentous marine cyanobacteria are extraordinarily rich sources of structurally novel, biomedically relevant natural products. To understand their biosynthetic origins as well as produce increased supplies and analog molecules, access to the clustered biosynthetic genes that encode for the assembly enzymes is necessary. Complicating these efforts is the universal presence of heterotrophic bacteria in the cell wall and sheath material of cyanobacteria obtained from the environment and those grown in uni-cyanobacterial culture. Moreover, the high similarity in genetic elements across disparate secondary metabolite biosynthetic pathways renders imprecise current gene cluster targeting strategies and contributes sequence complexity resulting in partial genome coverage. Thus, it was necessary to use a dual-method approach of single-cell genomic sequencing based on multiple displacement amplification (MDA) and metagenomic library screening. Here, we report the identification of the putative apratoxin. A biosynthetic gene cluster, a potent cancer cell cytotoxin with promise for medicinal applications. The roughly 58 kb biosynthetic gene cluster is composed of 12 open reading frames and has a type I modular mixed polyketide synthase/nonribosomal peptide synthetase (PKS/NRPS) organization and features loading and off-loading domain architecture never previously described. Moreover, this work represents the first successful isolation of a complete biosynthetic gene cluster from Lyngbya bouillonii, a tropical marine cyanobacterium renowned for its production of diverse bioactive secondary metabolites