about $< variable

[rishi nair]

hi all
in my makefile i write add an implicit rule like this

$(BUILD_DIR)/%.o:$(SRC_DIR)/$(patsubst %.obj,%.cxx,$(@F))
 $(CXX) $(CXXFLAGS) -o$@ $<

make generates the command as
cc cppflags -o <outputfile.o> srcdir/
cc cppflags -o <outputfile.o> srcdir/outputfile.cxx is expected
where am i going wrong.
my build env is cygwin/bash/gnumake
rishi