Laha Joydev K, Muthiah Chinnasamy, Taniguchi Masahiko, McDowell Brian E, Ptaszek Marcin, Lindsey Jonathan S
Department of Chemistry, North Carolina State University, Raleigh, North Carolina 27695-8204, USA.
J Org Chem. 2006 May 26;71(11):4092-102. doi: 10.1021/jo060208o.
Synthetic chlorins bearing diverse auxochromes at the 3- and 13-positions of the macrocycle are valuable targets given their resemblance to chlorophylls a and b, which bear 3-vinyl and 13-keto groups. A de novo route has been exploited to construct nine zinc chlorins bearing substituents at the 3- and 13-positions and two benchmark zinc chlorins lacking such substituents. The chlorins are sterically uncongested and bear (1) a geminal dimethyl group in the reduced pyrroline ring, (2) a H, an acetyl, a triisopropylsilylethynyl (TIPS-ethynyl), or a vinyl at the 3-position, (3) a H, an acetyl, or TIPS-ethynyl at the 13-position, and (4) a H or a mesityl at the 10-position. The synthesis of the 13-substituted chlorins relied on p-TsOH x H2O-catalyzed condensation of an 8,9-dibromo-1-formyldipyrromethane (eastern half) and 2,3,4,5-tetrahydro-1,3,3-trimethyldipyrrin (western half), followed by metal-mediated oxidative cyclization, affording the 13-bromochlorin. Similar use of a bromo- or TIPS-ethynyl-substituted western half provided access to 3-substituted chlorins. A 3-bromo, 13-bromo, or 3,13-dibromochlorin was further transformed by Pd-coupling to introduce the vinyl group (via tributylvinyltin), TIPS-ethynyl group (via TIPS-acetylene), or acetyl group (via tributyl(1-ethoxyvinyl)tin, followed by acidic hydrolysis). In the 10-mesityl-substituted zinc chlorins, the series of substituents, 3-vinyl, 13-TIPS-ethynyl, 3-TIPS-ethynyl, 13-acetyl, 3,13-bis(TIPS-ethynyl), 3-TIPS-ethynyl-13-acetyl, or 3,13-diacetyl, progressively causes (1) a redshift in the absorption maximum of the B band (405-436 nm) and the Q(y) band (606-662 nm), (2) a relative increase in the intensity of the Q(y) band (I(B)/I(Q) = 4.2-1.5), and (3) an increase in the fluorescence quantum yield phi(f) (0.059-0.29). The zinc chlorins bearing a 3-TIPS-ethynyl-13-acetyl or a 3,13-diacetyl group exhibit a number of spectral properties resembling those of chlorophyll a or its zinc analogue. Taken together, this study provides access to finely tuned chlorins for spectroscopic studies and diverse applications.
鉴于在大环的3-位和13-位带有不同助色团的合成二氢卟吩与叶绿素a和b相似（叶绿素a和b分别带有3-乙烯基和13-酮基），它们是有价值的研究对象。已开发出一种从头合成路线来构建9种在3-位和13-位带有取代基的锌二氢卟吩以及2种缺乏此类取代基的基准锌二氢卟吩。这些二氢卟吩在空间上没有拥挤现象，并且带有：(1) 在还原的吡咯啉环中的偕二甲基；(2) 在3-位的一个氢原子、一个乙酰基、一个三异丙基甲硅烷基乙炔基（TIPS-乙炔基）或一个乙烯基；(3) 在13-位的一个氢原子、一个乙酰基或TIPS-乙炔基；以及(4) 在10-位的一个氢原子或一个均三甲苯基。13-取代二氢卟吩的合成依赖于对甲苯磺酸一水合物催化的8,9-二溴-1-甲酰基二吡咯甲烷（东半部分）与2,3,4,5-四氢-1,3,3-三甲基二吡咯（西半部分）的缩合反应，随后进行金属介导的氧化环化反应，得到13-溴二氢卟吩。类似地，使用溴代或TIPS-乙炔基取代的西半部分可得到3-取代二氢卟吩。通过钯偶联进一步将3-溴、13-溴或3,13-二溴二氢卟吩进行转化，以引入乙烯基（通过三丁基乙烯基锡）、TIPS-乙炔基（通过TIPS-乙炔）或乙酰基（通过三丁基(1-乙氧基乙烯基)锡，随后进行酸性水解）。在10-均三甲苯基取代的锌二氢卟吩中，一系列取代基，即3-乙烯基、13-TIPS-乙炔基、3-TIPS-乙炔基、13-乙酰基、3,13-双(TIPS-乙炔基)、3-TIPS-乙炔基-13-乙酰基或3,13-二乙酰基，逐渐导致：(1) B带（405 - 436 nm）和Q(y)带（606 - 662 nm）的最大吸收发生红移；(2) Q(y)带的强度相对增加（I(B)/I(Q) = 4.2 - 1.5）；以及(3) 荧光量子产率φ(f)增加（0.059 - 0.29）。带有3-TIPS-乙炔基-13-乙酰基或3,13-二乙酰基的锌二氢卟吩表现出许多类似于叶绿素a或其锌类似物的光谱性质。综上所述，本研究为光谱研究和各种应用提供了可精细调节的二氢卟吩。
