•A distal isobranch in a long-chain terminal alkyne influences the rate of isomerization.•Alkyne 9 isomerizes 2.1 times faster than alkyne 5 at 55 °C.•The distal isobranch disrupts the coiling to allow more rapid deprotonation.•Simple energy calculations indicated that coiled 9 was about 2.4 kJ higher in energy.•The DMSO contained 4.38% of water.When compared to a long-straight chain terminal alkyne, a long chain terminal alkyne with a distal isopropyl unit (isobranched) isomerizes about two times faster when treated with strong base under identical conditions, and appears to follow pseudo first order kinetics. In both cases, equilibration to a 95–97:5–3 mixture of terminal:internal alkyne accompanies isomerization. The difference in rate may be due to an unusual folding of both long-chain alkynes, bringing the distal substituent close to the carbon-carbon-triple bond moiety. The distal isopropyl moiety may provide unanticipated steric hindrance that disrupts such folding, making the propargylic proton more available for reaction with base.Download high-res image (27KB)Download full-size image

Extending our previous work with 2-nitroimidazole-indocyanine dye-conjugate 4, we prepared the 4-nitroimidazole-piperazine-indocyanine derivative (6). We also prepared imidazole derivative 5 as a control. We compared the in vivo hypoxia targeting performance of both 5 and 6 with the previously tested 4, and 6 showed a higher fluorescent intensity after 15 min post-injection, about 1.5-fold higher than 4 and 2.5-fold higher than 5. Cells treated with 6 under hypoxic conditions showed a higher fluorescence yield when compared to the cells kept under normoxic conditions. All findings were supported with fluorescence images of histological sections of tumor samples using a Li-COR scanner and an immunohistochemistry technique for tumor hypoxia.

A periodontal pathogen, Porphyromonas gingivalis, produces two serine dipeptide lipid classes that we labeled lipid 654 and lipid 430, and both contain l-serine as the terminal amino acid. The lipid 654 and lipid 430 classes are each comprised of three species with differing fatty acid substitutions, but the most abundant species demonstrate unit masses of either 654 or 430, respectively. Recently we observed that the lipid 654 can be hydrolyzed by specific lipases to lipid 430. However, a substantial percentage of the naturally occurring lipid 654 cannot be enzymatically hydrolyzed to lipid 430. The observed partial hydrolysis could be due to the presence of a mixture of stereoisomers. Testing this theory requires structural verification of our so-called 654 and 430 by total synthesis. We present herein details of the convergent synthesis of lipids 430 and 654, which confirm the proposed structure of P. gingivalis lipid 654 to be (3R and 3S)-l-serine-2. The bis(fatty acid) (3R)-l-serine-2 was prepared as well as the synthetic precursor, serine dipeptide mono-fatty acid (3R)-l-serine-1, which is the structure of lipid 430. We also synthesized the (3S)-l-serine-2 diastereomer as well as (3S)-l-serine-1. Using these synthetic standards, we confirmed that PLA2-mediated hydrolysis of lipid 654 is enantioselective in that only the (3R)-l-serine-2, but not (3S)-l-serine 2 is enzymatically hydrolyzed.We have proven the structure of lipid 654, isolated from the dental pathogen Porphyromonas gingivalis. The lipid was prepared by a convergent synthetic route that is significantly shorter than other published routes, producing the targeted compound in higher yield. Further, we have shown that this dipeptide-lipid is selectivity hydrolyzed by lipase, consistent with results from lipid 654 obtained from P. gingivalis.

Tumor hypoxia is associated with the rapid proliferation and growth of malignant tumors, and the ability to detect tumor hypoxia is important for predicting tumor response to anti-cancer treatments. We have developed a class of dye-conjugates that are related to indocyanine green (ICG, 1) to target tumor hypoxia, based on in vivo infrared fluorescence imaging using nitroimidazole moieties linked to indocyanine fluorescent dyes. We previously reported that linking 2-nitroimidazole to an indocyanine dicarboxylic acid dye derivative (2) using an ethanolamine linker (ethanolamine-2-nitroimidazole-ICG, 3), led to a dye-conjugate that gave promising results for targeting cancer hypoxia in vivo. Structural modification of the dye conjugate replaced the ethanolamine unit with a piperazineacetyl unit and led a second generation dye conjugate, piperzine-2-nitroimidazole-ICG (4). This second generation dye-conjugate showed improved targeting of tumor hypoxia when compared with 3. Based on the hypothesis that molecules with more planar and rigid structures have a higher fluorescence yield, as they could release less absorbed energy through molecular vibration or collision, we have developed a new 2-nitroimidazole ICG conjugate, 12, with two carbon atoms less in the polyene linker. Dye-conjugate 12 was prepared from our new dye (8), and coupled to 2-nitroimidazole using a piperazine linker to produce this third-generation dye-conjugate. Spectral measurements showed that the absorption/emission wavelengths of 657/670 were shifted ∼100 nm from the second-generation hypoxia dye of 755/780 nm. Its fluorescence quantum yield was measured to be 0.467, which is about 5 times higher than that of 4 (0.083). In vivo experiments were conducted with balb/c mice and 12 showed more than twice the average in vivo fluorescence intensity in the tumor beyond two hours post retro-orbital injection as compared with 4. These initial results suggest that 12 may significantly improve in vivo tumor hypoxia targeting.

We have prepared a series of indocyanine green dicarboxylic acid derivatives (9a,b, 4, 10, 13) with modified polyene linkers in an attempt to increase the structural rigidity of the polyene linker and thereby the fluorescent yield. Incorporation of five- and six-membered rings into the polyene system led to lower florescent yield for 9a,b, 4 and 10, but shortening the chain by two carbon atoms led to an increase in fluorescent yield for 13.

We have successfully synthesized imidazole-dye conjugates by linking imidazole and nitroimidazoleacetic acids to an indocyanine green (ICG) carboxylic acid derivative, using an ethanolamine linker. These dye-conjugates show absorbance peaks at 754–756 nm and fluorescence peaks at 780 nm. The dye-conjugates show a blue shift of 25 nm and 30 nm in the absorption and fluorescence spectra respectively when compared to that of standard cardiogreen. There is no change in absorption and fluorescence spectral profiles between the ICG derivative and imidazole conjugates. The extinction coefficients of new ICG derivative and imidazole conjugates are 1.8 times higher than that of standard ICG. The relative quantum yields of the new compounds are 4.5–5.5 times higher than that of the Sigma–Aldrich’s ICG. The dyes are tested for hypoxia in-vitro with 4T1 luc cell lines and it is found that the cells treated with 2-nitroimidazole ICG show a contrast of fluorescence signal of 2.5–3.0 for the cells under hypoxic to that of cells under normoxic. However pure ICG shows no significant difference between hypoxic and normoxic cells.

The polymer PEDOT+ (1 or 2) mediates a cyclodehydration reaction with alditols 3, 5, 7, 9, in hydrocarbon solvents, to give cyclic ethers 4, 6, 8, or 10, respectively, in high yield with a trivial isolation protocol. Polymers 1 or 2 also mediate the cyclodehydration of ketohexoses such as d-fructose, but not aldohexoses, to the important industrial intermediate 5-hydroxymethylfurfural (17), under milder conditions when compared to reactions mediated by mineral acids. A cascade reaction with ketohexoses is observed in toluene via cyclodehydration followed by Friedel–Crafts alkylation of the initially formed benzylic alcohol to give 16.

l- And d-glutamic acids, as well as trans-4-hydroxy-l-proline, are converted to the corresponding 3-guaninyl-5-hydroxymethyl-2-pyrrolidinone (4) or 3-adeninyl-5-hydroxymethyl-2-pyrrolidinone (5) nucleoside analog. The protecting group used to block the lactam nitrogen in key intermediates has a significant effect on the diastereoselectivity of the coupling reaction with adenine or guanine.

Films of sorbitol-treated PEDOT–PSS or sorbitol-treated PEDOT (oxidized form) undergo a cyclodehydration reaction in the presence of the polymer to form 1,6-anhydrosorbitol. We offer evidence that both sorbitol and 1,6-anhydrosorbitol remain in the film and contribute to the enhanced conductivity. This reaction offers a new explanation for the observed “loss” of sorbitol upon annealing, and should be considered in any explanation of the role of sorbitol as an additive for PEDOT–PSS.

Contrary to previous reports in the literature, the reaction of polyhydric alcohols such as sorbitol or mannitol gives good yields of the tetrahydroxyoxepane derivative in the presence of an acid catalyst, in refluxing toluene, with complete retention of stereochemistry.

Porphyromonas gingivalis, a recognized periodontal pathogen, is a source of sphinganine bases, fatty acids, free ceramides as well as complex lipids that potentiate interleukin-1b-mediated secretory responses in gingival fibroblasts. The purpose of this study is the structural verification of the sphinganine bases and fatty acids that had been proposed as major components of the complex lipids found in P. gingivalis. The putative C17, C18, and C19 sphinganine bases were prepared from Garner's aldehyde (1) or from a protected serine Weinreb's amide (2). We confirmed that isobranched sphinganine bases are the major structural feature of the ceramides observed from P. gingivalis. We also prepared a C17 unsaturated fatty acid, along with an isobranched C17 3-hydroxy fatty acid, and determined that the major component of the active lipids was the latter.

Porphyromonas gingivalis, a recognized periodontal pathogen, is a source of sphinganine bases, fatty acids, free ceramides as well as complex lipids that potentiate interleukin-1b-mediated secretory responses in gingival fibroblasts. The purpose of this study is the structural verification of the sphinganine bases and fatty acids that had been proposed as major components of the complex lipids found in P. gingivalis. The putative C17, C18, and C19 sphinganine bases were prepared from Garner's aldehyde (1) or from a protected serine Weinreb's amide (2). We confirmed that isobranched sphinganine bases are the major structural feature of the ceramides observed from P. gingivalis. We also prepared a C17 unsaturated fatty acid, along with an isobranched C17 3-hydroxy fatty acid, and determined that the major component of the active lipids was the latter.

Tumor hypoxia is associated with the rapid proliferation and growth of malignant tumors, and the ability to detect tumor hypoxia is important for predicting tumor response to anti-cancer treatments. We have developed a class of dye-conjugates that are related to indocyanine green (ICG, 1) to target tumor hypoxia, based on in vivo infrared fluorescence imaging using nitroimidazole moieties linked to indocyanine fluorescent dyes. We previously reported that linking 2-nitroimidazole to an indocyanine dicarboxylic acid dye derivative (2) using an ethanolamine linker (ethanolamine-2-nitroimidazole-ICG, 3), led to a dye-conjugate that gave promising results for targeting cancer hypoxia in vivo. Structural modification of the dye conjugate replaced the ethanolamine unit with a piperazineacetyl unit and led a second generation dye conjugate, piperzine-2-nitroimidazole-ICG (4). This second generation dye-conjugate showed improved targeting of tumor hypoxia when compared with 3. Based on the hypothesis that molecules with more planar and rigid structures have a higher fluorescence yield, as they could release less absorbed energy through molecular vibration or collision, we have developed a new 2-nitroimidazole ICG conjugate, 12, with two carbon atoms less in the polyene linker. Dye-conjugate 12 was prepared from our new dye (8), and coupled to 2-nitroimidazole using a piperazine linker to produce this third-generation dye-conjugate. Spectral measurements showed that the absorption/emission wavelengths of 657/670 were shifted ∼100 nm from the second-generation hypoxia dye of 755/780 nm. Its fluorescence quantum yield was measured to be 0.467, which is about 5 times higher than that of 4 (0.083). In vivo experiments were conducted with balb/c mice and 12 showed more than twice the average in vivo fluorescence intensity in the tumor beyond two hours post retro-orbital injection as compared with 4. These initial results suggest that 12 may significantly improve in vivo tumor hypoxia targeting.